Rails Lighthouse ticket #3486

2-3-stable-unique-constraints.patch

From f259b38eee1b2a14507868e835f2ac187263a616 Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Wed, 11 Nov 2009 13:31:34 -0700
Subject: [PATCH] Friendly ActiveRecord error handling for db-enforced unique constraints

---
 activerecord/lib/active_record.rb                  |    1 +
 activerecord/lib/active_record/base.rb             |    4 ++
 .../connection_adapters/abstract_adapter.rb        |    7 +++
 .../connection_adapters/mysql_adapter.rb           |   12 ++++++
 .../connection_adapters/postgresql_adapter.rb      |    7 +++
 .../connection_adapters/sqlite_adapter.rb          |    7 +++
 activerecord/lib/active_record/locale/en.yml       |    2 +
 .../lib/active_record/unique_constraints.rb        |   24 ++++++++++++
 activerecord/test/cases/adapter_test.rb            |   35 +++++++++++++++++
 activerecord/test/cases/unique_constraints_test.rb |   40 ++++++++++++++++++++
 activerecord/test/models/unique_item.rb            |    2 +
 activerecord/test/schema/schema.rb                 |   15 +++++++
 12 files changed, 156 insertions(+), 0 deletions(-)
 create mode 100644 activerecord/lib/active_record/unique_constraints.rb
 create mode 100644 activerecord/test/cases/unique_constraints_test.rb
 create mode 100644 activerecord/test/models/unique_item.rb

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 2f8c5c7..8469255 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -68,6 +68,7 @@ module ActiveRecord
   autoload :TestCase, 'active_record/test_case'
   autoload :Timestamp, 'active_record/timestamp'
   autoload :Transactions, 'active_record/transactions'
+  autoload :UniqueConstraints, 'active_record/unique_constraints'
   autoload :Validations, 'active_record/validations'
 
   module Locking
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index d6b264c..1fe6bf8 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3177,6 +3177,10 @@ module ActiveRecord #:nodoc:
     include AutosaveAssociation, NestedAttributes
 
     include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
+
+    # UniqueConstraints needs to be included after Transactions, because we need #save_with_unique_constraints
+    # to rescue after the transaction has been resolved for postgres.
+    include UniqueConstraints
   end
 end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 6b7b363..6adea19 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -197,6 +197,13 @@ module ActiveRecord
         end
       end
 
+      # given an ActiveRecord::RecordNotUnique exception and a table name this returns the index whose
+      # unique constraint was violated, or nil if it can't determine the index
+      def index_for_record_not_unique(not_unique_exception, table_name) #:nodoc:
+        # override in derived class
+        nil
+      end
+
       protected
         def log(sql, name)
           if block_given?
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 5414a1d..635a8fc 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -571,6 +571,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
 
         def translate_exception(exception, message)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index b1cac88..c313082 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -941,6 +941,13 @@ module ActiveRecord
         sql.replace "SELECT * FROM (#{sql}) AS id_list ORDER BY #{order}"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/unique constraint "(\w+)"/)
+          index_name = match[1]
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         # Returns the version of the connected PostgreSQL version.
         def postgresql_version
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 79eea1d..31519f1 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -315,6 +315,13 @@ module ActiveRecord
         "INSERT INTO #{table_name} VALUES(NULL)"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/column(?:s)? (.*) (?:is|are) not unique/)
+          index_columns = match[1].split(', ')
+          indexes(table_name).detect { |i| i.columns == index_columns }
+        end
+      end
+
       protected
         def select(sql, name = nil) #:nodoc:
           execute(sql, name).map do |row|
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 2813524..a7dec95 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -15,6 +15,8 @@ en:
         too_short: "is too short (minimum is {{count}} characters)"
         wrong_length: "is the wrong length (should be {{count}} characters)"
         taken: "has already been taken"
+        taken_multiple: "has already been taken for {{context}}"
+        taken_generic: "Unique requirement not met"
         not_a_number: "is not a number"
         greater_than: "must be greater than {{count}}"
         greater_than_or_equal_to: "must be greater than or equal to {{count}}"
diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
new file mode 100644
index 0000000..99e6353
--- /dev/null
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -0,0 +1,24 @@
+module ActiveRecord
+  # See ActiveRecord::Transactions::ClassMethods for documentation.
+  module UniqueConstraints
+    def self.included(base)
+      base.class_eval do
+        alias_method_chain :save, :unique_constraints
+      end
+    end
+
+    def save_with_unique_constraints(perform_validation = true) #:nodoc:
+      save_without_unique_constraints(perform_validation)
+    rescue ActiveRecord::RecordNotUnique => e
+      index = connection.index_for_record_not_unique(e.original_exception, self.class.table_name)
+      if !index
+        errors.add_to_base(I18n.translate(:'activerecord.errors.messages.taken_generic'))
+      elsif index.columns.size == 1
+        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+      else
+        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+      end
+      false
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 4797112..0883ea0 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -157,4 +157,39 @@ class AdapterTest < ActiveRecord::TestCase
       end
     end
   end
+
+  # tests for db-enforced unique constraints
+  unique_scenarios = {
+    :single         => {:sql => "INSERT INTO unique_items(uniq) VALUES('abc')",
+                        :expected => ['uniq']},
+    :single_named   => {:sql => "INSERT INTO unique_items(uniq_named) VALUES('abc')",
+                        :expected => ['uniq_named']},
+    :multiple       => {:sql => "INSERT INTO unique_items(uniq_1, uniq_2, uniq_3) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1', 'uniq_2', 'uniq_3']},
+    :multiple_named => {:sql => "INSERT INTO unique_items(uniq_1_named, uniq_2_named, uniq_3_named) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1_named', 'uniq_2_named', 'uniq_3_named']}
+  }
+  unique_scenarios.each do |name, data|
+    test "finds index for unique constraint #{name}" do
+      @connection.execute data[:sql]
+      exception = get_exception(ActiveRecord::RecordNotUnique) do
+        @connection.execute data[:sql]
+      end
+      # postgres can't query indexes until transaction is rolled back
+      @connection.rollback_db_transaction if current_adapter?(:PostgreSQLAdapter)
+      assert_equal data[:expected], @connection.index_for_record_not_unique(exception, 'unique_items').columns
+    end
+  end
+
+  protected
+
+  def get_exception(expected_exception)
+    begin
+      yield
+    rescue expected_exception => e
+      e
+    else
+      flunk "Expected #{expected_exception} exception"
+    end
+  end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
new file mode 100644
index 0000000..2b5d0ee
--- /dev/null
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -0,0 +1,40 @@
+require "cases/helper"
+require 'models/unique_item'
+
+class UniquenessValidationTest < ActiveRecord::TestCase
+
+  def test_validate_uniqueness_on_create
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    invalid_item = UniqueItem.create(:uniq => 'abc')
+    assert_equal "has already been taken", invalid_item.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_save
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    item_2.save
+    assert_equal "has already been taken", item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_update
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.update_attributes(:uniq => item_1.uniq)
+    assert_equal "has already been taken", item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_multiple
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal "has already been taken for uniq_2/uniq_3", invalid_item.errors[:uniq_1]
+  end
+
+  def test_validate_uniqueness_generic
+    ActiveRecord::Base.connection.expects(:index_for_record_not_unique).returns(nil)
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal "Unique requirement not met", invalid_item.errors[:base]
+  end
+
+end
\ No newline at end of file
diff --git a/activerecord/test/models/unique_item.rb b/activerecord/test/models/unique_item.rb
new file mode 100644
index 0000000..3c6f6f0
--- /dev/null
+++ b/activerecord/test/models/unique_item.rb
@@ -0,0 +1,2 @@
+class UniqueItem < ActiveRecord::Base
+end
\ No newline at end of file
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 984c5ba..8d64e51 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -479,6 +479,21 @@ ActiveRecord::Schema.define do
     end
   end
 
+  create_table :unique_items, :force => true do |t|
+    t.string :uniq
+    t.string :uniq_1
+    t.string :uniq_2
+    t.string :uniq_3
+    t.string :uniq_named
+    t.string :uniq_1_named
+    t.string :uniq_2_named
+    t.string :uniq_3_named
+  end
+  add_index :unique_items, [:uniq], :unique => true
+  add_index :unique_items, [:uniq_named], :unique => true, :name => 'unique_named_single_index'
+  add_index :unique_items, [:uniq_1, :uniq_2, :uniq_3], :unique => true
+  add_index :unique_items, [:uniq_1_named, :uniq_2_named, :uniq_3_named], :unique => true, :name => 'unique_named_multiple_index'
+
   except 'SQLite' do
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, :force => true do |t|
-- 
1.6.1.2

master-unique-constraints.patch

From 466ce19b2989324be1fca05b5b553700997b6803 Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Wed, 11 Nov 2009 11:34:27 -0700
Subject: [PATCH] Friendly ActiveRecord error handling for db-enforced unique constraints

---
 activerecord/lib/active_record.rb                  |    1 +
 activerecord/lib/active_record/base.rb             |    4 ++
 .../connection_adapters/abstract_adapter.rb        |    7 +++
 .../connection_adapters/mysql_adapter.rb           |   12 ++++++
 .../connection_adapters/postgresql_adapter.rb      |    7 +++
 .../connection_adapters/sqlite_adapter.rb          |    7 +++
 activerecord/lib/active_record/locale/en.yml       |    2 +
 .../lib/active_record/unique_constraints.rb        |   24 ++++++++++++
 activerecord/test/cases/adapter_test.rb            |   35 +++++++++++++++++
 activerecord/test/cases/unique_constraints_test.rb |   40 ++++++++++++++++++++
 activerecord/test/models/unique_item.rb            |    2 +
 activerecord/test/schema/schema.rb                 |   15 +++++++
 12 files changed, 156 insertions(+), 0 deletions(-)
 create mode 100644 activerecord/lib/active_record/unique_constraints.rb
 create mode 100644 activerecord/test/cases/unique_constraints_test.rb
 create mode 100644 activerecord/test/models/unique_item.rb

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 8195e78..0aac5be 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -70,6 +70,7 @@ module ActiveRecord
   autoload :TestCase, 'active_record/test_case'
   autoload :Timestamp, 'active_record/timestamp'
   autoload :Transactions, 'active_record/transactions'
+  autoload :UniqueConstraints, 'active_record/unique_constraints'
   autoload :Types, 'active_record/types'
   autoload :Validations, 'active_record/validations'
 
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 056f29f..e2efb2a 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3094,6 +3094,10 @@ module ActiveRecord #:nodoc:
 
     include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
 
+    # UniqueConstraints needs to be included after Transactions, because we need #save_with_unique_constraints
+    # to rescue after the transaction has been resolved for postgres.
+    include UniqueConstraints
+
   end
 end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 8fae26b..832b962 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -198,6 +198,13 @@ module ActiveRecord
         end
       end
 
+      # given an ActiveRecord::RecordNotUnique exception and a table name this returns the index whose
+      # unique constraint was violated, or nil if it can't determine the index
+      def index_for_record_not_unique(not_unique_exception, table_name) #:nodoc:
+        # override in derived class
+        nil
+      end
+
       protected
         def log(sql, name, &block)
           ActiveSupport::Notifications.instrument(:sql, :sql => sql, :name => name, &block)
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index ad36ff2..3ca7608 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -561,6 +561,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
 
         def translate_exception(exception, message)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 1d52c5e..70bbbd8 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -929,6 +929,13 @@ module ActiveRecord
         sql << order_columns * ', '
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/unique constraint "(\w+)"/)
+          index_name = match[1]
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         # Returns the version of the connected PostgreSQL version.
         def postgresql_version
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index c9c2892..72dc049 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -294,6 +294,13 @@ module ActiveRecord
         "VALUES(NULL)"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/column(?:s)? (.*) (?:is|are) not unique/)
+          index_columns = match[1].split(', ')
+          indexes(table_name).detect { |i| i.columns == index_columns }
+        end
+      end
+
       protected
         def select(sql, name = nil) #:nodoc:
           execute(sql, name).map do |row|
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 092f5f0..8144735 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -15,6 +15,8 @@ en:
         too_short: "is too short (minimum is {{count}} characters)"
         wrong_length: "is the wrong length (should be {{count}} characters)"
         taken: "has already been taken"
+        taken_multiple: "has already been taken for {{context}}"
+        taken_generic: "Unique requirement not met"
         not_a_number: "is not a number"
         greater_than: "must be greater than {{count}}"
         greater_than_or_equal_to: "must be greater than or equal to {{count}}"
diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
new file mode 100644
index 0000000..7a17b6a
--- /dev/null
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -0,0 +1,24 @@
+module ActiveRecord
+  # See ActiveRecord::Transactions::ClassMethods for documentation.
+  module UniqueConstraints
+    def self.included(base)
+      base.class_eval do
+        alias_method_chain :save, :unique_constraints
+      end
+    end
+
+    def save_with_unique_constraints(perform_validation = true) #:nodoc:
+      save_without_unique_constraints(perform_validation)
+    rescue ActiveRecord::RecordNotUnique => e
+      index = connection.index_for_record_not_unique(e, self.class.table_name)
+      if !index
+        errors[:base] << I18n.translate(:'activerecord.errors.messages.taken_generic')
+      elsif index.columns.size == 1
+        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+      else
+        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+      end
+      false
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index c59be26..4c8f58b 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -142,4 +142,39 @@ class AdapterTest < ActiveRecord::TestCase
       end
     end
   end
+
+  # tests for db-enforced unique constraints
+  unique_scenarios = {
+    :single         => {:sql => "INSERT INTO unique_items(uniq) VALUES('abc')",
+                        :expected => ['uniq']},
+    :single_named   => {:sql => "INSERT INTO unique_items(uniq_named) VALUES('abc')",
+                        :expected => ['uniq_named']},
+    :multiple       => {:sql => "INSERT INTO unique_items(uniq_1, uniq_2, uniq_3) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1', 'uniq_2', 'uniq_3']},
+    :multiple_named => {:sql => "INSERT INTO unique_items(uniq_1_named, uniq_2_named, uniq_3_named) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1_named', 'uniq_2_named', 'uniq_3_named']}
+  }
+  unique_scenarios.each do |name, data|
+    test "finds index for unique constraint #{name}" do
+      @connection.execute data[:sql]
+      exception = get_exception(ActiveRecord::RecordNotUnique) do
+        @connection.execute data[:sql]
+      end
+      # postgres can't query indexes until transaction is rolled back
+      @connection.rollback_db_transaction if current_adapter?(:PostgreSQLAdapter)
+      assert_equal data[:expected], @connection.index_for_record_not_unique(exception, 'unique_items').columns
+    end
+  end
+
+  protected
+
+  def get_exception(expected_exception)
+    begin
+      yield
+    rescue expected_exception => e
+      e
+    else
+      flunk "Expected #{expected_exception} exception"
+    end
+  end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
new file mode 100644
index 0000000..92ba6d8
--- /dev/null
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -0,0 +1,40 @@
+require "cases/helper"
+require 'models/unique_item'
+
+class UniquenessValidationTest < ActiveRecord::TestCase
+
+  def test_validate_uniqueness_on_create
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    invalid_item = UniqueItem.create(:uniq => 'abc')
+    assert_equal ["has already been taken"], invalid_item.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_save
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    item_2.save
+    assert_equal ["has already been taken"], item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_update
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.update_attributes(:uniq => item_1.uniq)
+    assert_equal ["has already been taken"], item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_multiple
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal ["has already been taken for uniq_2/uniq_3"], invalid_item.errors[:uniq_1]
+  end
+
+  def test_validate_uniqueness_generic
+    ActiveRecord::Base.connection.expects(:index_for_record_not_unique).returns(nil)
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal ["Unique requirement not met"], invalid_item.errors[:base]
+  end
+
+end
\ No newline at end of file
diff --git a/activerecord/test/models/unique_item.rb b/activerecord/test/models/unique_item.rb
new file mode 100644
index 0000000..3c6f6f0
--- /dev/null
+++ b/activerecord/test/models/unique_item.rb
@@ -0,0 +1,2 @@
+class UniqueItem < ActiveRecord::Base
+end
\ No newline at end of file
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 15e5e12..a2b3da4 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -532,6 +532,21 @@ ActiveRecord::Schema.define do
     t.string :title
   end
 
+  create_table :unique_items, :force => true do |t|
+    t.string :uniq
+    t.string :uniq_1
+    t.string :uniq_2
+    t.string :uniq_3
+    t.string :uniq_named
+    t.string :uniq_1_named
+    t.string :uniq_2_named
+    t.string :uniq_3_named
+  end
+  add_index :unique_items, [:uniq], :unique => true
+  add_index :unique_items, [:uniq_named], :unique => true, :name => 'unique_named_single_index'
+  add_index :unique_items, [:uniq_1, :uniq_2, :uniq_3], :unique => true
+  add_index :unique_items, [:uniq_1_named, :uniq_2_named, :uniq_3_named], :unique => true, :name => 'unique_named_multiple_index'
+
   except 'SQLite' do
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, :force => true do |t|
-- 
1.6.1.2

unique-patch-2-3-stable.diff

From 5573e913b8651ea53ae6d94686b4b63f2cca2e83 Mon Sep 17 00:00:00 2001
From: Michael Schuerig <michael@schuerig.de>
Date: Sun, 5 Apr 2009 01:19:29 +0200
Subject: [PATCH 1/4] Translate adapter errors that indicate a violated uniqueness constraint to ActiveRecord::RecordNotUnique exception derived from ActiveReecord::StatementInvalid.

Signed-off-by: Michael Koziarski <michael@koziarski.com>
---
 activerecord/lib/active_record/base.rb             |    4 ++++
 .../connection_adapters/abstract_adapter.rb        |    7 ++++++-
 .../connection_adapters/mysql_adapter.rb           |   11 +++++++++++
 .../connection_adapters/postgresql_adapter.rb      |    9 +++++++++
 .../connection_adapters/sqlite_adapter.rb          |   10 ++++++++++
 activerecord/test/cases/adapter_test.rb            |    7 +++++++
 6 files changed, 47 insertions(+), 1 deletions(-)

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 4929969..27b645d 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -55,6 +55,10 @@ module ActiveRecord #:nodoc:
   class StatementInvalid < ActiveRecordError
   end
 
+  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
+  class RecordNotUnique < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
   # does not match number of expected variables.
   #
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 22871f2..6b7b363 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -216,9 +216,14 @@ module ActiveRecord
           @last_verification = 0
           message = "#{e.class.name}: #{e.message}: #{sql}"
           log_info(message, name, 0)
-          raise ActiveRecord::StatementInvalid, message
+          raise translate_exception(e, message)
         end
 
+      def translate_exception(e, message)
+        # override in derived class
+        ActiveRecord::StatementInvalid.new(message)
+      end
+
         def format_log_entry(message, dump = nil)
           if ActiveRecord::Base.colorize_logging
             if @@row_even
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index a8aa16e..8625395 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -586,6 +586,17 @@ module ActiveRecord
         where_sql
       end
 
+      protected
+
+        def translate_exception(exception, message)
+          case exception.errno
+          when 1062
+            RecordNotUnique.new(message)
+          else
+            super
+          end
+        end
+
       private
         def connect
           encoding = @config[:encoding]
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index bc289ff..4bd7e4a 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -958,6 +958,15 @@ module ActiveRecord
             end
         end
 
+        def translate_exception(exception, message)
+          case exception.message
+          when /duplicate key value violates unique constraint/
+            RecordNotUnique.new(message)
+          else
+            super
+          end
+        end
+
       private
         # The internal PostgreSQL identifier of the money data type.
         MONEY_COLUMN_TYPE_OID = 790 #:nodoc:
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 0bf97a9..88831ee 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -435,6 +435,16 @@ module ActiveRecord
             'INTEGER PRIMARY KEY NOT NULL'.freeze
           end
         end
+
+        def translate_exception(exception, message)
+          case exception.message
+          when /column(s)? .* (is|are) not unique/
+            RecordNotUnique.new(message)
+          else
+            super
+          end
+        end
+
     end
 
     class SQLite2Adapter < SQLiteAdapter # :nodoc:
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 3dd3dd8..27d1625 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -142,4 +142,11 @@ class AdapterTest < ActiveRecord::TestCase
       assert_equal " LIMIT 1,7 OFFSET 7", @connection.add_limit_offset!("", :limit=>sql_inject, :offset=>7)
     end
   end
+
+  def test_uniqueness_violations_are_translated_to_specific_exception
+    @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
+    assert_raises(ActiveRecord::RecordNotUnique) do
+      @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
+    end
+  end
 end
-- 
1.6.1.2


From 1b69f6d39bbb35be22de771261426bfdb2b0459e Mon Sep 17 00:00:00 2001
From: Michael Schuerig <michael@schuerig.de>
Date: Sun, 5 Apr 2009 01:42:21 +0200
Subject: [PATCH 2/4] Translate foreign key violations to ActiveRecord::InvalidForeignKey exceptions.

Signed-off-by: Michael Koziarski <michael@koziarski.com>
---
 activerecord/lib/active_record/base.rb             |    4 ++++
 .../connection_adapters/mysql_adapter.rb           |    2 ++
 .../connection_adapters/postgresql_adapter.rb      |    2 ++
 activerecord/test/cases/adapter_test.rb            |    8 ++++++++
 4 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 27b645d..57c1d6d 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -59,6 +59,10 @@ module ActiveRecord #:nodoc:
   class RecordNotUnique < StatementInvalid
   end
 
+  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  class InvalidForeignKey < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
   # does not match number of expected variables.
   #
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 8625395..ac3dfda 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -592,6 +592,8 @@ module ActiveRecord
           case exception.errno
           when 1062
             RecordNotUnique.new(message)
+          when 1452
+            InvalidForeignKey.new(message)
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 4bd7e4a..4ab06e8 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -962,6 +962,8 @@ module ActiveRecord
           case exception.message
           when /duplicate key value violates unique constraint/
             RecordNotUnique.new(message)
+          when /violates foreign key constraint/
+            InvalidForeignKey.new(message)
           else
             super
           end
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 27d1625..4797112 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -149,4 +149,12 @@ class AdapterTest < ActiveRecord::TestCase
       @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
     end
   end
+
+  def test_foreign_key_violations_are_translated_to_specific_exception
+    unless @connection.adapter_name == 'SQLite'
+      assert_raises(ActiveRecord::InvalidForeignKey) do
+        @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (0)"
+      end
+    end
+  end
 end
-- 
1.6.1.2


From edffa1bda17cca21e84cc953ebbabae4d295d0db Mon Sep 17 00:00:00 2001
From: Michael Koziarski <michael@koziarski.com>
Date: Fri, 26 Jun 2009 16:59:27 +1200
Subject: [PATCH 3/4] Make sure the wrapped exceptions also have the original exception available.

[#2419 state:committed]
---
 activerecord/lib/active_record/base.rb             |   15 +++++++++++++--
 .../connection_adapters/mysql_adapter.rb           |    4 ++--
 .../connection_adapters/postgresql_adapter.rb      |    4 ++--
 .../connection_adapters/sqlite_adapter.rb          |    2 +-
 4 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 57c1d6d..7c8c866 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -55,12 +55,23 @@ module ActiveRecord #:nodoc:
   class StatementInvalid < ActiveRecordError
   end
 
+  # Parent class for all specific exceptions which wrap database driver exceptions
+  # provides access to the original exception also.
+  class WrappedDatabaseException < StatementInvalid
+    attr_reader :original_exception
+
+    def initialize(message, original_exception)
+      super(message)
+      @original_exception, = original_exception
+    end
+  end
+
   # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
-  class RecordNotUnique < StatementInvalid
+  class RecordNotUnique < WrappedDatabaseException
   end
 
   # Raised when a record cannot be inserted or updated because it references a non-existent record.
-  class InvalidForeignKey < StatementInvalid
+  class InvalidForeignKey < WrappedDatabaseException
   end
 
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index ac3dfda..1fffec8 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -591,9 +591,9 @@ module ActiveRecord
         def translate_exception(exception, message)
           case exception.errno
           when 1062
-            RecordNotUnique.new(message)
+            RecordNotUnique.new(message, exception)
           when 1452
-            InvalidForeignKey.new(message)
+            InvalidForeignKey.new(message, exception)
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 4ab06e8..b1cac88 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -961,9 +961,9 @@ module ActiveRecord
         def translate_exception(exception, message)
           case exception.message
           when /duplicate key value violates unique constraint/
-            RecordNotUnique.new(message)
+            RecordNotUnique.new(message, exception)
           when /violates foreign key constraint/
-            InvalidForeignKey.new(message)
+            InvalidForeignKey.new(message, exception)
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 88831ee..79eea1d 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -439,7 +439,7 @@ module ActiveRecord
         def translate_exception(exception, message)
           case exception.message
           when /column(s)? .* (is|are) not unique/
-            RecordNotUnique.new(message)
+            RecordNotUnique.new(message, exception)
           else
             super
           end
-- 
1.6.1.2


From 5dc2eb5d07f8e999f0c9d0d3932a5a7d5bce2dae Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Wed, 11 Nov 2009 13:31:34 -0700
Subject: [PATCH 4/4] Friendly ActiveRecord error handling for db-enforced unique constraints

---
 activerecord/lib/active_record.rb                  |    1 +
 activerecord/lib/active_record/base.rb             |    4 ++
 .../connection_adapters/abstract_adapter.rb        |    7 +++
 .../connection_adapters/mysql_adapter.rb           |   12 ++++++
 .../connection_adapters/postgresql_adapter.rb      |    7 +++
 .../connection_adapters/sqlite_adapter.rb          |    7 +++
 activerecord/lib/active_record/locale/en.yml       |    2 +
 .../lib/active_record/unique_constraints.rb        |   24 ++++++++++++
 activerecord/test/cases/adapter_test.rb            |   35 +++++++++++++++++
 activerecord/test/cases/unique_constraints_test.rb |   40 ++++++++++++++++++++
 activerecord/test/models/unique_item.rb            |    2 +
 activerecord/test/schema/schema.rb                 |   15 +++++++
 12 files changed, 156 insertions(+), 0 deletions(-)
 create mode 100644 activerecord/lib/active_record/unique_constraints.rb
 create mode 100644 activerecord/test/cases/unique_constraints_test.rb
 create mode 100644 activerecord/test/models/unique_item.rb

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 2f8c5c7..8469255 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -68,6 +68,7 @@ module ActiveRecord
   autoload :TestCase, 'active_record/test_case'
   autoload :Timestamp, 'active_record/timestamp'
   autoload :Transactions, 'active_record/transactions'
+  autoload :UniqueConstraints, 'active_record/unique_constraints'
   autoload :Validations, 'active_record/validations'
 
   module Locking
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 7c8c866..da9c110 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3200,6 +3200,10 @@ module ActiveRecord #:nodoc:
     include AutosaveAssociation, NestedAttributes
 
     include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
+
+    # UniqueConstraints needs to be included after Transactions, because we need #save_with_unique_constraints
+    # to rescue after the transaction has been resolved for postgres.
+    include UniqueConstraints
   end
 end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 6b7b363..6adea19 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -197,6 +197,13 @@ module ActiveRecord
         end
       end
 
+      # given an ActiveRecord::RecordNotUnique exception and a table name this returns the index whose
+      # unique constraint was violated, or nil if it can't determine the index
+      def index_for_record_not_unique(not_unique_exception, table_name) #:nodoc:
+        # override in derived class
+        nil
+      end
+
       protected
         def log(sql, name)
           if block_given?
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 1fffec8..658df1f 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -586,6 +586,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
 
         def translate_exception(exception, message)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index b1cac88..c313082 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -941,6 +941,13 @@ module ActiveRecord
         sql.replace "SELECT * FROM (#{sql}) AS id_list ORDER BY #{order}"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/unique constraint "(\w+)"/)
+          index_name = match[1]
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         # Returns the version of the connected PostgreSQL version.
         def postgresql_version
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 79eea1d..31519f1 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -315,6 +315,13 @@ module ActiveRecord
         "INSERT INTO #{table_name} VALUES(NULL)"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/column(?:s)? (.*) (?:is|are) not unique/)
+          index_columns = match[1].split(', ')
+          indexes(table_name).detect { |i| i.columns == index_columns }
+        end
+      end
+
       protected
         def select(sql, name = nil) #:nodoc:
           execute(sql, name).map do |row|
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 2813524..a7dec95 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -15,6 +15,8 @@ en:
         too_short: "is too short (minimum is {{count}} characters)"
         wrong_length: "is the wrong length (should be {{count}} characters)"
         taken: "has already been taken"
+        taken_multiple: "has already been taken for {{context}}"
+        taken_generic: "Unique requirement not met"
         not_a_number: "is not a number"
         greater_than: "must be greater than {{count}}"
         greater_than_or_equal_to: "must be greater than or equal to {{count}}"
diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
new file mode 100644
index 0000000..99e6353
--- /dev/null
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -0,0 +1,24 @@
+module ActiveRecord
+  # See ActiveRecord::Transactions::ClassMethods for documentation.
+  module UniqueConstraints
+    def self.included(base)
+      base.class_eval do
+        alias_method_chain :save, :unique_constraints
+      end
+    end
+
+    def save_with_unique_constraints(perform_validation = true) #:nodoc:
+      save_without_unique_constraints(perform_validation)
+    rescue ActiveRecord::RecordNotUnique => e
+      index = connection.index_for_record_not_unique(e.original_exception, self.class.table_name)
+      if !index
+        errors.add_to_base(I18n.translate(:'activerecord.errors.messages.taken_generic'))
+      elsif index.columns.size == 1
+        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+      else
+        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+      end
+      false
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 4797112..0883ea0 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -157,4 +157,39 @@ class AdapterTest < ActiveRecord::TestCase
       end
     end
   end
+
+  # tests for db-enforced unique constraints
+  unique_scenarios = {
+    :single         => {:sql => "INSERT INTO unique_items(uniq) VALUES('abc')",
+                        :expected => ['uniq']},
+    :single_named   => {:sql => "INSERT INTO unique_items(uniq_named) VALUES('abc')",
+                        :expected => ['uniq_named']},
+    :multiple       => {:sql => "INSERT INTO unique_items(uniq_1, uniq_2, uniq_3) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1', 'uniq_2', 'uniq_3']},
+    :multiple_named => {:sql => "INSERT INTO unique_items(uniq_1_named, uniq_2_named, uniq_3_named) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1_named', 'uniq_2_named', 'uniq_3_named']}
+  }
+  unique_scenarios.each do |name, data|
+    test "finds index for unique constraint #{name}" do
+      @connection.execute data[:sql]
+      exception = get_exception(ActiveRecord::RecordNotUnique) do
+        @connection.execute data[:sql]
+      end
+      # postgres can't query indexes until transaction is rolled back
+      @connection.rollback_db_transaction if current_adapter?(:PostgreSQLAdapter)
+      assert_equal data[:expected], @connection.index_for_record_not_unique(exception, 'unique_items').columns
+    end
+  end
+
+  protected
+
+  def get_exception(expected_exception)
+    begin
+      yield
+    rescue expected_exception => e
+      e
+    else
+      flunk "Expected #{expected_exception} exception"
+    end
+  end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
new file mode 100644
index 0000000..2b5d0ee
--- /dev/null
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -0,0 +1,40 @@
+require "cases/helper"
+require 'models/unique_item'
+
+class UniquenessValidationTest < ActiveRecord::TestCase
+
+  def test_validate_uniqueness_on_create
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    invalid_item = UniqueItem.create(:uniq => 'abc')
+    assert_equal "has already been taken", invalid_item.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_save
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    item_2.save
+    assert_equal "has already been taken", item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_update
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.update_attributes(:uniq => item_1.uniq)
+    assert_equal "has already been taken", item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_multiple
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal "has already been taken for uniq_2/uniq_3", invalid_item.errors[:uniq_1]
+  end
+
+  def test_validate_uniqueness_generic
+    ActiveRecord::Base.connection.expects(:index_for_record_not_unique).returns(nil)
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal "Unique requirement not met", invalid_item.errors[:base]
+  end
+
+end
\ No newline at end of file
diff --git a/activerecord/test/models/unique_item.rb b/activerecord/test/models/unique_item.rb
new file mode 100644
index 0000000..3c6f6f0
--- /dev/null
+++ b/activerecord/test/models/unique_item.rb
@@ -0,0 +1,2 @@
+class UniqueItem < ActiveRecord::Base
+end
\ No newline at end of file
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index b046104..17a6fc4 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -499,6 +499,21 @@ ActiveRecord::Schema.define do
     t.string :title
   end
 
+  create_table :unique_items, :force => true do |t|
+    t.string :uniq
+    t.string :uniq_1
+    t.string :uniq_2
+    t.string :uniq_3
+    t.string :uniq_named
+    t.string :uniq_1_named
+    t.string :uniq_2_named
+    t.string :uniq_3_named
+  end
+  add_index :unique_items, [:uniq], :unique => true
+  add_index :unique_items, [:uniq_named], :unique => true, :name => 'unique_named_single_index'
+  add_index :unique_items, [:uniq_1, :uniq_2, :uniq_3], :unique => true
+  add_index :unique_items, [:uniq_1_named, :uniq_2_named, :uniq_3_named], :unique => true, :name => 'unique_named_multiple_index'
+
   except 'SQLite' do
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, :force => true do |t|
-- 
1.6.1.2

unique-patch-2-3-stable.patch

From 48fcff95ae1b5e55837e81a4c132a3c208a235f8 Mon Sep 17 00:00:00 2001
From: Michael Schuerig <michael@schuerig.de>
Date: Sun, 5 Apr 2009 01:19:29 +0200
Subject: [PATCH 1/5] Translate adapter errors that indicate a violated uniqueness constraint to ActiveRecord::RecordNotUnique exception derived from ActiveReecord::StatementInvalid.

Signed-off-by: Michael Koziarski <michael@koziarski.com>
---
 activerecord/lib/active_record/base.rb             |    4 ++++
 .../connection_adapters/abstract_adapter.rb        |    7 ++++++-
 .../connection_adapters/mysql_adapter.rb           |    9 +++++++++
 .../connection_adapters/postgresql_adapter.rb      |    9 +++++++++
 .../connection_adapters/sqlite_adapter.rb          |   10 ++++++++++
 activerecord/test/cases/adapter_test.rb            |    7 +++++++
 6 files changed, 45 insertions(+), 1 deletions(-)

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index ac82cc1..94468a4 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -56,6 +56,10 @@ module ActiveRecord #:nodoc:
   class StatementInvalid < ActiveRecordError
   end
 
+  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
+  class RecordNotUnique < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
   # does not match number of expected variables.
   #
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index b8a6a71..6d21960 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -224,9 +224,14 @@ module ActiveRecord
           @last_verification = 0
           message = "#{e.class.name}: #{e.message}: #{sql}"
           log_info(message, name, 0)
-          raise ActiveRecord::StatementInvalid, message
+          raise translate_exception(e, message)
         end
 
+      def translate_exception(e, message)
+        # override in derived class
+        ActiveRecord::StatementInvalid.new(message)
+      end
+
         def format_log_entry(message, dump = nil)
           if ActiveRecord::Base.colorize_logging
             if @@row_even
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 6f41f84..62d9417 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -602,6 +602,15 @@ module ActiveRecord
           end
         end
 
+        def translate_exception(exception, message)
+          case exception.errno
+          when 1062
+            RecordNotUnique.new(message)
+          else
+            super
+          end
+        end
+
       private
         def connect
           encoding = @config[:encoding]
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index a348318..66afc3c 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -931,6 +931,15 @@ module ActiveRecord
             end
         end
 
+        def translate_exception(exception, message)
+          case exception.message
+          when /duplicate key value violates unique constraint/
+            RecordNotUnique.new(message)
+          else
+            super
+          end
+        end
+
       private
         # The internal PostgreSQL identifier of the money data type.
         MONEY_COLUMN_TYPE_OID = 790 #:nodoc:
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 1616698..e0d04e6 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -436,6 +436,16 @@ module ActiveRecord
             'INTEGER PRIMARY KEY NOT NULL'.freeze
           end
         end
+
+        def translate_exception(exception, message)
+          case exception.message
+          when /column(s)? .* (is|are) not unique/
+            RecordNotUnique.new(message)
+          else
+            super
+          end
+        end
+
     end
 
     class SQLite2Adapter < SQLiteAdapter # :nodoc:
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index b7fa6df..2118c10 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -141,4 +141,11 @@ class AdapterTest < ActiveRecord::TestCase
       assert_equal " LIMIT 1,7 OFFSET 7", @connection.add_limit_offset!("", :limit=>sql_inject, :offset=>7)
     end
   end
+
+  def test_uniqueness_violations_are_translated_to_specific_exception
+    @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
+    assert_raises(ActiveRecord::RecordNotUnique) do
+      @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
+    end
+  end
 end
-- 
1.7.2.1


From 9efed026a931dc4203b4332b0951b8b09c669476 Mon Sep 17 00:00:00 2001
From: Michael Schuerig <michael@schuerig.de>
Date: Sun, 5 Apr 2009 01:42:21 +0200
Subject: [PATCH 2/5] Translate foreign key violations to ActiveRecord::InvalidForeignKey exceptions.

Signed-off-by: Michael Koziarski <michael@koziarski.com>
---
 activerecord/lib/active_record/base.rb             |    4 ++++
 .../connection_adapters/mysql_adapter.rb           |    2 ++
 .../connection_adapters/postgresql_adapter.rb      |    2 ++
 activerecord/test/cases/adapter_test.rb            |    8 ++++++++
 4 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 94468a4..c42b1ab 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -60,6 +60,10 @@ module ActiveRecord #:nodoc:
   class RecordNotUnique < StatementInvalid
   end
 
+  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  class InvalidForeignKey < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
   # does not match number of expected variables.
   #
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 62d9417..e49908b 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -606,6 +606,8 @@ module ActiveRecord
           case exception.errno
           when 1062
             RecordNotUnique.new(message)
+          when 1452
+            InvalidForeignKey.new(message)
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 66afc3c..d79aea5 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -935,6 +935,8 @@ module ActiveRecord
           case exception.message
           when /duplicate key value violates unique constraint/
             RecordNotUnique.new(message)
+          when /violates foreign key constraint/
+            InvalidForeignKey.new(message)
           else
             super
           end
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 2118c10..7a9a289 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -148,4 +148,12 @@ class AdapterTest < ActiveRecord::TestCase
       @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
     end
   end
+
+  def test_foreign_key_violations_are_translated_to_specific_exception
+    unless @connection.adapter_name == 'SQLite'
+      assert_raises(ActiveRecord::InvalidForeignKey) do
+        @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (0)"
+      end
+    end
+  end
 end
-- 
1.7.2.1


From 3d2796f98d7f2c33bb63f6c2f2026588b99fb2c9 Mon Sep 17 00:00:00 2001
From: Michael Koziarski <michael@koziarski.com>
Date: Fri, 26 Jun 2009 16:59:27 +1200
Subject: [PATCH 3/5] Make sure the wrapped exceptions also have the original exception available.

[#2419 state:committed]
---
 activerecord/lib/active_record/base.rb             |   15 +++++++++++++--
 .../connection_adapters/mysql_adapter.rb           |    4 ++--
 .../connection_adapters/postgresql_adapter.rb      |    4 ++--
 .../connection_adapters/sqlite_adapter.rb          |    2 +-
 4 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index c42b1ab..9fc1ea5 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -56,12 +56,23 @@ module ActiveRecord #:nodoc:
   class StatementInvalid < ActiveRecordError
   end
 
+  # Parent class for all specific exceptions which wrap database driver exceptions
+  # provides access to the original exception also.
+  class WrappedDatabaseException < StatementInvalid
+    attr_reader :original_exception
+
+    def initialize(message, original_exception)
+      super(message)
+      @original_exception, = original_exception
+    end
+  end
+
   # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
-  class RecordNotUnique < StatementInvalid
+  class RecordNotUnique < WrappedDatabaseException
   end
 
   # Raised when a record cannot be inserted or updated because it references a non-existent record.
-  class InvalidForeignKey < StatementInvalid
+  class InvalidForeignKey < WrappedDatabaseException
   end
 
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index e49908b..0ecab7b 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -605,9 +605,9 @@ module ActiveRecord
         def translate_exception(exception, message)
           case exception.errno
           when 1062
-            RecordNotUnique.new(message)
+            RecordNotUnique.new(message, exception)
           when 1452
-            InvalidForeignKey.new(message)
+            InvalidForeignKey.new(message, exception)
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index d79aea5..590a4f1 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -934,9 +934,9 @@ module ActiveRecord
         def translate_exception(exception, message)
           case exception.message
           when /duplicate key value violates unique constraint/
-            RecordNotUnique.new(message)
+            RecordNotUnique.new(message, exception)
           when /violates foreign key constraint/
-            InvalidForeignKey.new(message)
+            InvalidForeignKey.new(message, exception)
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index e0d04e6..ae1ffa0 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -440,7 +440,7 @@ module ActiveRecord
         def translate_exception(exception, message)
           case exception.message
           when /column(s)? .* (is|are) not unique/
-            RecordNotUnique.new(message)
+            RecordNotUnique.new(message, exception)
           else
             super
           end
-- 
1.7.2.1


From 11a16a9838ecabfb25f5fc89e93bdc3d7b25c4bf Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Wed, 11 Nov 2009 13:31:34 -0700
Subject: [PATCH 4/5] Friendly ActiveRecord error handling for db-enforced unique constraints

---
 activerecord/lib/active_record.rb                  |    1 +
 activerecord/lib/active_record/base.rb             |    1 +
 .../connection_adapters/abstract_adapter.rb        |    7 +++
 .../connection_adapters/mysql_adapter.rb           |   12 ++++++
 .../connection_adapters/postgresql_adapter.rb      |   13 ++++++
 .../connection_adapters/sqlite_adapter.rb          |    7 +++
 activerecord/lib/active_record/locale/en.yml       |    2 +
 .../lib/active_record/unique_constraints.rb        |   30 +++++++++++++++
 activerecord/test/cases/adapter_test.rb            |   35 +++++++++++++++++
 activerecord/test/cases/unique_constraints_test.rb |   40 ++++++++++++++++++++
 activerecord/test/models/unique_item.rb            |    2 +
 activerecord/test/schema/schema.rb                 |   15 +++++++
 12 files changed, 165 insertions(+), 0 deletions(-)
 create mode 100644 activerecord/lib/active_record/unique_constraints.rb
 create mode 100644 activerecord/test/cases/unique_constraints_test.rb
 create mode 100644 activerecord/test/models/unique_item.rb

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 0d0ada9..3404c16 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -68,6 +68,7 @@ module ActiveRecord
   autoload :TestCase, 'active_record/test_case'
   autoload :Timestamp, 'active_record/timestamp'
   autoload :Transactions, 'active_record/transactions'
+  autoload :UniqueConstraints, 'active_record/unique_constraints'
   autoload :Validations, 'active_record/validations'
 
   module Locking
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 9fc1ea5..2e79954 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3230,6 +3230,7 @@ module ActiveRecord #:nodoc:
     include AutosaveAssociation, NestedAttributes
 
     include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
+    include UniqueConstraints
   end
 end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 6d21960..c7e8269 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -199,6 +199,13 @@ module ActiveRecord
         end
       end
 
+      # given an ActiveRecord::RecordNotUnique exception and a table name this returns the index whose
+      # unique constraint was violated, or nil if it can't determine the index
+      def index_for_record_not_unique(not_unique_exception, table_name) #:nodoc:
+        # override in derived class
+        nil
+      end
+
       protected
         def log(sql, name)
           if block_given?
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 0ecab7b..64f8f87 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -588,6 +588,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         def quoted_columns_for_index(column_names, options = {})
           length = options[:length] if options.is_a?(Hash)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 590a4f1..2eb3fce 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -669,6 +669,12 @@ module ActiveRecord
         indexes
       end
 
+      # postgres doesn't let us query this in the middle of an aborted transaction so caching can come in handy
+      def cached_indexes(table_name)
+        @cached_indexes ||= {}
+        @cached_indexes[table_name] ||= indexes(table_name)
+      end
+
       # Returns the list of all column definitions for a table.
       def columns(table_name, name = nil)
         # Limit, precision, and scale are all handled by the superclass.
@@ -914,6 +920,13 @@ module ActiveRecord
         sql.replace "SELECT * FROM (#{sql}) AS id_list ORDER BY #{order}"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/unique constraint "(\w+)"/)
+          index_name = match[1]
+          cached_indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         # Returns the version of the connected PostgreSQL version.
         def postgresql_version
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index ae1ffa0..a43f6d4 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -316,6 +316,13 @@ module ActiveRecord
         "INSERT INTO #{table_name} VALUES(NULL)"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/column(?:s)? (.*) (?:is|are) not unique/)
+          index_columns = match[1].split(', ')
+          indexes(table_name).detect { |i| i.columns == index_columns }
+        end
+      end
+
       protected
         def select(sql, name = nil) #:nodoc:
           execute(sql, name).map do |row|
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 6dab5e2..353fbda 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -15,6 +15,8 @@ en:
         too_short: "is too short (minimum is %{count} characters)"
         wrong_length: "is the wrong length (should be %{count} characters)"
         taken: "has already been taken"
+        taken_multiple: "has already been taken for %{context}"
+        taken_generic: "Unique requirement not met"
         not_a_number: "is not a number"
         greater_than: "must be greater than %{count}"
         greater_than_or_equal_to: "must be greater than or equal to %{count}"
diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
new file mode 100644
index 0000000..6702e37
--- /dev/null
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -0,0 +1,30 @@
+module ActiveRecord
+  # See ActiveRecord::Transactions::ClassMethods for documentation.
+  module UniqueConstraints
+    def self.included(base)
+      base.class_eval do
+        alias_method_chain :save, :unique_constraints
+      end
+    end
+
+    # work around postgres not allowing us to query indexes in the middle of an aborted transaction
+    def cache_indexes
+      connection.cached_indexes(self.class.table_name) if connection.respond_to?(:cached_indexes)
+    end
+
+    def save_with_unique_constraints(perform_validation = true) #:nodoc:
+      cache_indexes
+      save_without_unique_constraints(perform_validation)
+    rescue ActiveRecord::RecordNotUnique => e
+      index = connection.index_for_record_not_unique(e.original_exception, self.class.table_name)
+      if !index
+        errors.add_to_base(I18n.translate(:'activerecord.errors.messages.taken_generic'))
+      elsif index.columns.size == 1
+        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+      else
+        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+      end
+      false
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 7a9a289..f99e8d6 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -156,4 +156,39 @@ class AdapterTest < ActiveRecord::TestCase
       end
     end
   end
+
+  # tests for db-enforced unique constraints
+  unique_scenarios = {
+    :single         => {:sql => "INSERT INTO unique_items(uniq) VALUES('abc')",
+                        :expected => ['uniq']},
+    :single_named   => {:sql => "INSERT INTO unique_items(uniq_named) VALUES('abc')",
+                        :expected => ['uniq_named']},
+    :multiple       => {:sql => "INSERT INTO unique_items(uniq_1, uniq_2, uniq_3) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1', 'uniq_2', 'uniq_3']},
+    :multiple_named => {:sql => "INSERT INTO unique_items(uniq_1_named, uniq_2_named, uniq_3_named) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1_named', 'uniq_2_named', 'uniq_3_named']}
+  }
+  unique_scenarios.each do |name, data|
+    test "finds index for unique constraint #{name}" do
+      @connection.execute data[:sql]
+      exception = get_exception(ActiveRecord::RecordNotUnique) do
+        @connection.execute data[:sql]
+      end
+      # postgres can't query indexes until transaction is rolled back
+      @connection.rollback_db_transaction if current_adapter?(:PostgreSQLAdapter)
+      assert_equal data[:expected], @connection.index_for_record_not_unique(exception, 'unique_items').columns
+    end
+  end
+
+  protected
+
+  def get_exception(expected_exception)
+    begin
+      yield
+    rescue expected_exception => e
+      e
+    else
+      flunk "Expected #{expected_exception} exception"
+    end
+  end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
new file mode 100644
index 0000000..2b5d0ee
--- /dev/null
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -0,0 +1,40 @@
+require "cases/helper"
+require 'models/unique_item'
+
+class UniquenessValidationTest < ActiveRecord::TestCase
+
+  def test_validate_uniqueness_on_create
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    invalid_item = UniqueItem.create(:uniq => 'abc')
+    assert_equal "has already been taken", invalid_item.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_save
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    item_2.save
+    assert_equal "has already been taken", item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_update
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.update_attributes(:uniq => item_1.uniq)
+    assert_equal "has already been taken", item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_multiple
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal "has already been taken for uniq_2/uniq_3", invalid_item.errors[:uniq_1]
+  end
+
+  def test_validate_uniqueness_generic
+    ActiveRecord::Base.connection.expects(:index_for_record_not_unique).returns(nil)
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal "Unique requirement not met", invalid_item.errors[:base]
+  end
+
+end
\ No newline at end of file
diff --git a/activerecord/test/models/unique_item.rb b/activerecord/test/models/unique_item.rb
new file mode 100644
index 0000000..3c6f6f0
--- /dev/null
+++ b/activerecord/test/models/unique_item.rb
@@ -0,0 +1,2 @@
+class UniqueItem < ActiveRecord::Base
+end
\ No newline at end of file
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 2e5299c..acd1f02 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -536,6 +536,21 @@ ActiveRecord::Schema.define do
     t.string :title
   end
 
+  create_table :unique_items, :force => true do |t|
+    t.string :uniq
+    t.string :uniq_1
+    t.string :uniq_2
+    t.string :uniq_3
+    t.string :uniq_named
+    t.string :uniq_1_named
+    t.string :uniq_2_named
+    t.string :uniq_3_named
+  end
+  add_index :unique_items, [:uniq], :unique => true
+  add_index :unique_items, [:uniq_named], :unique => true, :name => 'unique_named_single_index'
+  add_index :unique_items, [:uniq_1, :uniq_2, :uniq_3], :unique => true
+  add_index :unique_items, [:uniq_1_named, :uniq_2_named, :uniq_3_named], :unique => true, :name => 'unique_named_multiple_index'
+
   except 'SQLite' do
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, :force => true do |t|
-- 
1.7.2.1


From 14feddfdda9a7fd3709c099a458bd4f8e81aea59 Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Fri, 15 Jan 2010 15:10:55 -0700
Subject: [PATCH 5/5] Add bang method handling to db-enforced unique constraints

---
 .../lib/active_record/unique_constraints.rb        |   30 ++++++++++++++-----
 activerecord/test/cases/unique_constraints_test.rb |   30 ++++++++++++++++++++
 2 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
index 6702e37..b3c1234 100644
--- a/activerecord/lib/active_record/unique_constraints.rb
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -4,6 +4,7 @@ module ActiveRecord
     def self.included(base)
       base.class_eval do
         alias_method_chain :save, :unique_constraints
+        alias_method_chain :save!, :unique_constraints
       end
     end
 
@@ -16,15 +17,28 @@ module ActiveRecord
       cache_indexes
       save_without_unique_constraints(perform_validation)
     rescue ActiveRecord::RecordNotUnique => e
-      index = connection.index_for_record_not_unique(e.original_exception, self.class.table_name)
-      if !index
-        errors.add_to_base(I18n.translate(:'activerecord.errors.messages.taken_generic'))
-      elsif index.columns.size == 1
-        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
-      else
-        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
-      end
+      parse_unique_exception(e)
       false
     end
+
+    def save_with_unique_constraints! #:nodoc:
+      cache_indexes
+      save_without_unique_constraints!
+    rescue ActiveRecord::RecordNotUnique => e
+      parse_unique_exception(e)
+      raise RecordInvalid.new(self)
+    end
+
+    protected
+      def parse_unique_exception(e)
+        index = connection.index_for_record_not_unique(e.original_exception, self.class.table_name)
+        if !index
+          errors.add_to_base(I18n.translate(:'activerecord.errors.messages.taken_generic'))
+        elsif index.columns.size == 1
+          errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+        else
+          errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+        end
+      end
   end
 end
\ No newline at end of file
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
index 2b5d0ee..8adae04 100644
--- a/activerecord/test/cases/unique_constraints_test.rb
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -9,6 +9,12 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal "has already been taken", invalid_item.errors[:uniq]
   end
 
+  def test_validate_uniqueness_on_create!
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    e = get_unique_exception { UniqueItem.create!(:uniq => 'abc') }
+    assert_equal "has already been taken", e.record.errors[:uniq]
+  end
+
   def test_validate_uniqueness_on_save
     item_1 = UniqueItem.create!(:uniq => 'abc')
     item_2 = UniqueItem.create!(:uniq => 'xyz')
@@ -17,6 +23,14 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal "has already been taken", item_2.errors[:uniq]
   end
 
+  def test_validate_uniqueness_on_save!
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    e = get_unique_exception { item_2.save! }
+    assert_equal("has already been taken", e.record.errors[:uniq])
+  end
+
   def test_validate_uniqueness_on_update
     item_1 = UniqueItem.create!(:uniq => 'abc')
     item_2 = UniqueItem.create!(:uniq => 'xyz')
@@ -24,6 +38,13 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal "has already been taken", item_2.errors[:uniq]
   end
 
+  def test_validate_uniqueness_on_update!
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    e = get_unique_exception { item_2.update_attributes!(:uniq => item_1.uniq) }
+    assert_equal("has already been taken", e.record.errors[:uniq])
+  end
+
   def test_validate_uniqueness_multiple
     valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
     invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
@@ -37,4 +58,13 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal "Unique requirement not met", invalid_item.errors[:base]
   end
 
+  protected
+    def get_unique_exception
+      yield
+    rescue ActiveRecord::RecordInvalid => e
+      e
+    else
+      flunk "Expected ActiveRecord::RecordInvalid exception"
+    end
+
 end
\ No newline at end of file
-- 
1.7.2.1

unique-patch-master.diff

From 5055887efe3f3d560003d14599e8c048059fa830 Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Tue, 22 Dec 2009 07:42:48 -0700
Subject: [PATCH] Friendly ActiveRecord error handling for db-enforced unique constraints

---
 activerecord/lib/active_record.rb                  |    1 +
 activerecord/lib/active_record/base.rb             |    4 ++
 .../connection_adapters/abstract_adapter.rb        |    7 +++
 .../connection_adapters/mysql_adapter.rb           |   12 ++++++
 .../connection_adapters/postgresql_adapter.rb      |    7 +++
 .../connection_adapters/sqlite_adapter.rb          |    7 +++
 activerecord/lib/active_record/locale/en.yml       |    2 +
 .../lib/active_record/unique_constraints.rb        |   24 ++++++++++++
 activerecord/test/cases/adapter_test.rb            |   35 +++++++++++++++++
 activerecord/test/cases/unique_constraints_test.rb |   40 ++++++++++++++++++++
 activerecord/test/models/unique_item.rb            |    2 +
 activerecord/test/schema/schema.rb                 |   15 +++++++
 12 files changed, 156 insertions(+), 0 deletions(-)
 create mode 100644 activerecord/lib/active_record/unique_constraints.rb
 create mode 100644 activerecord/test/cases/unique_constraints_test.rb
 create mode 100644 activerecord/test/models/unique_item.rb

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 2376bbd..f3cff35 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -68,6 +68,7 @@ module ActiveRecord
   autoload :Timestamp
   autoload :Transactions
   autoload :Types
+  autoload :UniqueConstraints
   autoload :Validations
 
   module AttributeMethods
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 321bba4..da52ec1 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3117,6 +3117,10 @@ module ActiveRecord #:nodoc:
 
     include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
 
+    # UniqueConstraints needs to be included after Transactions, because we need #save_with_unique_constraints
+    # to rescue after the transaction has been resolved for postgres.
+    include UniqueConstraints
+
   end
 end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 8fae26b..832b962 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -198,6 +198,13 @@ module ActiveRecord
         end
       end
 
+      # given an ActiveRecord::RecordNotUnique exception and a table name this returns the index whose
+      # unique constraint was violated, or nil if it can't determine the index
+      def index_for_record_not_unique(not_unique_exception, table_name) #:nodoc:
+        # override in derived class
+        nil
+      end
+
       protected
         def log(sql, name, &block)
           ActiveSupport::Notifications.instrument(:sql, :sql => sql, :name => name, &block)
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index fa28bc6..d83e3d0 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -576,6 +576,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
 
         def translate_exception(exception, message)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 1d52c5e..70bbbd8 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -929,6 +929,13 @@ module ActiveRecord
         sql << order_columns * ', '
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/unique constraint "(\w+)"/)
+          index_name = match[1]
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         # Returns the version of the connected PostgreSQL version.
         def postgresql_version
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index c9c2892..72dc049 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -294,6 +294,13 @@ module ActiveRecord
         "VALUES(NULL)"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/column(?:s)? (.*) (?:is|are) not unique/)
+          index_columns = match[1].split(', ')
+          indexes(table_name).detect { |i| i.columns == index_columns }
+        end
+      end
+
       protected
         def select(sql, name = nil) #:nodoc:
           execute(sql, name).map do |row|
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 092f5f0..8144735 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -15,6 +15,8 @@ en:
         too_short: "is too short (minimum is {{count}} characters)"
         wrong_length: "is the wrong length (should be {{count}} characters)"
         taken: "has already been taken"
+        taken_multiple: "has already been taken for {{context}}"
+        taken_generic: "Unique requirement not met"
         not_a_number: "is not a number"
         greater_than: "must be greater than {{count}}"
         greater_than_or_equal_to: "must be greater than or equal to {{count}}"
diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
new file mode 100644
index 0000000..7a17b6a
--- /dev/null
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -0,0 +1,24 @@
+module ActiveRecord
+  # See ActiveRecord::Transactions::ClassMethods for documentation.
+  module UniqueConstraints
+    def self.included(base)
+      base.class_eval do
+        alias_method_chain :save, :unique_constraints
+      end
+    end
+
+    def save_with_unique_constraints(perform_validation = true) #:nodoc:
+      save_without_unique_constraints(perform_validation)
+    rescue ActiveRecord::RecordNotUnique => e
+      index = connection.index_for_record_not_unique(e, self.class.table_name)
+      if !index
+        errors[:base] << I18n.translate(:'activerecord.errors.messages.taken_generic')
+      elsif index.columns.size == 1
+        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+      else
+        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+      end
+      false
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index c59be26..4c8f58b 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -142,4 +142,39 @@ class AdapterTest < ActiveRecord::TestCase
       end
     end
   end
+
+  # tests for db-enforced unique constraints
+  unique_scenarios = {
+    :single         => {:sql => "INSERT INTO unique_items(uniq) VALUES('abc')",
+                        :expected => ['uniq']},
+    :single_named   => {:sql => "INSERT INTO unique_items(uniq_named) VALUES('abc')",
+                        :expected => ['uniq_named']},
+    :multiple       => {:sql => "INSERT INTO unique_items(uniq_1, uniq_2, uniq_3) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1', 'uniq_2', 'uniq_3']},
+    :multiple_named => {:sql => "INSERT INTO unique_items(uniq_1_named, uniq_2_named, uniq_3_named) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1_named', 'uniq_2_named', 'uniq_3_named']}
+  }
+  unique_scenarios.each do |name, data|
+    test "finds index for unique constraint #{name}" do
+      @connection.execute data[:sql]
+      exception = get_exception(ActiveRecord::RecordNotUnique) do
+        @connection.execute data[:sql]
+      end
+      # postgres can't query indexes until transaction is rolled back
+      @connection.rollback_db_transaction if current_adapter?(:PostgreSQLAdapter)
+      assert_equal data[:expected], @connection.index_for_record_not_unique(exception, 'unique_items').columns
+    end
+  end
+
+  protected
+
+  def get_exception(expected_exception)
+    begin
+      yield
+    rescue expected_exception => e
+      e
+    else
+      flunk "Expected #{expected_exception} exception"
+    end
+  end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
new file mode 100644
index 0000000..92ba6d8
--- /dev/null
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -0,0 +1,40 @@
+require "cases/helper"
+require 'models/unique_item'
+
+class UniquenessValidationTest < ActiveRecord::TestCase
+
+  def test_validate_uniqueness_on_create
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    invalid_item = UniqueItem.create(:uniq => 'abc')
+    assert_equal ["has already been taken"], invalid_item.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_save
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    item_2.save
+    assert_equal ["has already been taken"], item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_update
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.update_attributes(:uniq => item_1.uniq)
+    assert_equal ["has already been taken"], item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_multiple
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal ["has already been taken for uniq_2/uniq_3"], invalid_item.errors[:uniq_1]
+  end
+
+  def test_validate_uniqueness_generic
+    ActiveRecord::Base.connection.expects(:index_for_record_not_unique).returns(nil)
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal ["Unique requirement not met"], invalid_item.errors[:base]
+  end
+
+end
\ No newline at end of file
diff --git a/activerecord/test/models/unique_item.rb b/activerecord/test/models/unique_item.rb
new file mode 100644
index 0000000..3c6f6f0
--- /dev/null
+++ b/activerecord/test/models/unique_item.rb
@@ -0,0 +1,2 @@
+class UniqueItem < ActiveRecord::Base
+end
\ No newline at end of file
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 0dd9da4..1aea762 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -532,6 +532,21 @@ ActiveRecord::Schema.define do
     t.string :title
   end
 
+  create_table :unique_items, :force => true do |t|
+    t.string :uniq
+    t.string :uniq_1
+    t.string :uniq_2
+    t.string :uniq_3
+    t.string :uniq_named
+    t.string :uniq_1_named
+    t.string :uniq_2_named
+    t.string :uniq_3_named
+  end
+  add_index :unique_items, [:uniq], :unique => true
+  add_index :unique_items, [:uniq_named], :unique => true, :name => 'unique_named_single_index'
+  add_index :unique_items, [:uniq_1, :uniq_2, :uniq_3], :unique => true
+  add_index :unique_items, [:uniq_1_named, :uniq_2_named, :uniq_3_named], :unique => true, :name => 'unique_named_multiple_index'
+
   except 'SQLite' do
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, :force => true do |t|
-- 
1.6.1.2

unique-patch-master.patch

From 9e300598ee86d318d5312478d398f2ebdd1db2c0 Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Tue, 9 Feb 2010 13:13:01 -0700
Subject: [PATCH 1/2] Friendly ActiveRecord error handling for db-enforced unique constraints

---
 activerecord/lib/active_record.rb                  |    1 +
 activerecord/lib/active_record/base.rb             |    1 +
 .../connection_adapters/abstract_adapter.rb        |    7 +++
 .../connection_adapters/mysql2_adapter.rb          |   12 ++++++
 .../connection_adapters/mysql_adapter.rb           |   12 ++++++
 .../connection_adapters/postgresql_adapter.rb      |   13 ++++++
 .../connection_adapters/sqlite_adapter.rb          |    7 +++
 activerecord/lib/active_record/locale/en.yml       |    2 +
 .../lib/active_record/unique_constraints.rb        |   29 ++++++++++++++
 activerecord/test/cases/adapter_test.rb            |   35 +++++++++++++++++
 activerecord/test/cases/unique_constraints_test.rb |   40 ++++++++++++++++++++
 activerecord/test/models/unique_item.rb            |    2 +
 activerecord/test/schema/schema.rb                 |   15 +++++++
 13 files changed, 176 insertions(+), 0 deletions(-)
 create mode 100644 activerecord/lib/active_record/unique_constraints.rb
 create mode 100644 activerecord/test/cases/unique_constraints_test.rb
 create mode 100644 activerecord/test/models/unique_item.rb

diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 5afb978..869c90b 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -78,6 +78,7 @@ module ActiveRecord
     autoload :SessionStore
     autoload :Timestamp
     autoload :Transactions
+    autoload :UniqueConstraints
     autoload :Validations
   end
 
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index effb17b..9909663 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -1940,6 +1940,7 @@ MSG
     # #save_with_autosave_associations to be wrapped inside a transaction.
     include AutosaveAssociation, NestedAttributes
     include Aggregations, Transactions, Reflection, Serialization
+    include UniqueConstraints
 
     NilClass.add_whiner(self) if NilClass.respond_to?(:add_whiner)
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 3a3a73f..43ffa46 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -207,6 +207,13 @@ module ActiveRecord
         "active_record_#{open_transactions}"
       end
 
+      # given an ActiveRecord::RecordNotUnique exception and a table name this returns the index whose
+      # unique constraint was violated, or nil if it can't determine the index
+      def index_for_record_not_unique(not_unique_exception, table_name) #:nodoc:
+        # override in derived class
+        nil
+      end
+
       protected
 
         def log(sql, name = "SQL")
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index acf1832..47da0da 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -536,6 +536,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         def quoted_columns_for_index(column_names, options = {})
           length = options[:length] if options.is_a?(Hash)
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index cdf1ebf..7c89aef 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -646,6 +646,18 @@ module ActiveRecord
         where_sql
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        case exception.message
+        when /Duplicate entry.*for key (\d+)/
+          index_position = $1.to_i
+          # minus two b/c mysql message is one-based + rails excludes primary key index from indexes list
+          indexes(table_name)[index_position - 2]
+        when /Duplicate entry.*for key '(\w+)'/
+          index_name = $1
+          indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         def quoted_columns_for_index(column_names, options = {})
           length = options[:length] if options.is_a?(Hash)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 46c0f3f..bea174b 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -708,6 +708,12 @@ module ActiveRecord
         end.compact
       end
 
+      # postgres doesn't let us query this in the middle of an aborted transaction so we sometimes need to cache beforehand
+      def cached_indexes(table_name) #:nodoc:
+        @cached_indexes ||= {}
+        @cached_indexes[table_name] ||= indexes(table_name)
+      end
+
       # Returns the list of all column definitions for a table.
       def columns(table_name, name = nil)
         # Limit, precision, and scale are all handled by the superclass.
@@ -944,6 +950,13 @@ module ActiveRecord
         sql << order_columns * ', '
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/unique constraint "(\w+)"/)
+          index_name = match[1]
+          cached_indexes(table_name).detect { |i| i.name == index_name }
+        end
+      end
+
       protected
         # Returns the version of the connected PostgreSQL version.
         def postgresql_version
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index f650a1b..02eebd8 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -340,6 +340,13 @@ module ActiveRecord
         "VALUES(NULL)"
       end
 
+      def index_for_record_not_unique(exception, table_name) #:nodoc:
+        if match = exception.message.match(/column(?:s)? (.*) (?:is|are) not unique/)
+          index_columns = match[1].split(', ')
+          indexes(table_name).detect { |i| i.columns == index_columns }
+        end
+      end
+
       protected
         def select(sql, name = nil, binds = []) #:nodoc:
           exec_query(sql, name, binds).to_a
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 44328f6..e310fba 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -9,6 +9,8 @@ en:
     errors:
       messages:
         taken: "has already been taken"
+        taken_multiple: "has already been taken for %{context}"
+        taken_generic: "Unique requirement not met"
         record_invalid: "Validation failed: %{errors}"
         # Append your own errors here or at the model/attributes scope.
 
diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
new file mode 100644
index 0000000..4a6d748
--- /dev/null
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -0,0 +1,29 @@
+module ActiveRecord
+  module UniqueConstraints
+    extend ActiveSupport::Concern
+
+    included do
+      alias_method_chain :save, :unique_constraints
+    end
+
+    # work around postgres not allowing us to query indexes in the middle of an aborted transaction
+    def cache_indexes #:nodoc:
+      connection.cached_indexes(self.class.table_name) if connection.respond_to?(:cached_indexes)
+    end
+
+    def save_with_unique_constraints(*args) #:nodoc:
+      cache_indexes
+      save_without_unique_constraints(*args)
+    rescue ActiveRecord::RecordNotUnique => e
+      index = connection.index_for_record_not_unique(e, self.class.table_name)
+      if !index
+        errors[:base] << I18n.t(:'activerecord.errors.messages.taken_generic')
+      elsif index.columns.size == 1
+        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+      else
+        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+      end
+      false
+    end
+  end
+end
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 49b2e94..1cb8b0a 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -141,4 +141,39 @@ class AdapterTest < ActiveRecord::TestCase
       end
     end
   end
+
+  # tests for db-enforced unique constraints
+  unique_scenarios = {
+    :single         => {:sql => "INSERT INTO unique_items(uniq) VALUES('abc')",
+                        :expected => ['uniq']},
+    :single_named   => {:sql => "INSERT INTO unique_items(uniq_named) VALUES('abc')",
+                        :expected => ['uniq_named']},
+    :multiple       => {:sql => "INSERT INTO unique_items(uniq_1, uniq_2, uniq_3) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1', 'uniq_2', 'uniq_3']},
+    :multiple_named => {:sql => "INSERT INTO unique_items(uniq_1_named, uniq_2_named, uniq_3_named) VALUES('a', 'b', 'c')",
+                        :expected => ['uniq_1_named', 'uniq_2_named', 'uniq_3_named']}
+  }
+  unique_scenarios.each do |name, data|
+    test "finds index for unique constraint #{name}" do
+      @connection.execute data[:sql]
+      exception = get_exception(ActiveRecord::RecordNotUnique) do
+        @connection.execute data[:sql]
+      end
+      # postgres can't query indexes until transaction is rolled back
+      @connection.rollback_db_transaction if current_adapter?(:PostgreSQLAdapter)
+      assert_equal data[:expected], @connection.index_for_record_not_unique(exception, 'unique_items').columns
+    end
+  end
+
+  protected
+
+  def get_exception(expected_exception)
+    begin
+      yield
+    rescue expected_exception => e
+      e
+    else
+      flunk "Expected #{expected_exception} exception"
+    end
+  end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
new file mode 100644
index 0000000..18d1890
--- /dev/null
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -0,0 +1,40 @@
+require "cases/helper"
+require 'models/unique_item'
+
+class UniquenessValidationTest < ActiveRecord::TestCase
+
+  def test_validate_uniqueness_on_create
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    invalid_item = UniqueItem.create(:uniq => 'abc')
+    assert_equal ["has already been taken"], invalid_item.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_save
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    item_2.save
+    assert_equal ["has already been taken"], item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_on_update
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.update_attributes(:uniq => item_1.uniq)
+    assert_equal ["has already been taken"], item_2.errors[:uniq]
+  end
+
+  def test_validate_uniqueness_multiple
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal ["has already been taken for uniq_2/uniq_3"], invalid_item.errors[:uniq_1]
+  end
+
+  def test_validate_uniqueness_generic
+    ActiveRecord::Base.connection.expects(:index_for_record_not_unique).returns(nil)
+    valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
+    assert_equal ["Unique requirement not met"], invalid_item.errors[:base]
+  end
+
+end
diff --git a/activerecord/test/models/unique_item.rb b/activerecord/test/models/unique_item.rb
new file mode 100644
index 0000000..e805cb8
--- /dev/null
+++ b/activerecord/test/models/unique_item.rb
@@ -0,0 +1,2 @@
+class UniqueItem < ActiveRecord::Base
+end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 326c336..d408154 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -668,6 +668,21 @@ ActiveRecord::Schema.define do
     t.string :name
   end
 
+  create_table :unique_items, :force => true do |t|
+    t.string :uniq
+    t.string :uniq_1
+    t.string :uniq_2
+    t.string :uniq_3
+    t.string :uniq_named
+    t.string :uniq_1_named
+    t.string :uniq_2_named
+    t.string :uniq_3_named
+  end
+  add_index :unique_items, [:uniq], :unique => true
+  add_index :unique_items, [:uniq_named], :unique => true, :name => 'unique_named_single_index'
+  add_index :unique_items, [:uniq_1, :uniq_2, :uniq_3], :unique => true
+  add_index :unique_items, [:uniq_1_named, :uniq_2_named, :uniq_3_named], :unique => true, :name => 'unique_named_multiple_index'
+
   except 'SQLite' do
     # fk_test_has_fk should be before fk_test_has_pk
     create_table :fk_test_has_fk, :force => true do |t|
-- 
1.7.2.1


From fb06e862fc2cb5d48717d6af948466fb40cb002d Mon Sep 17 00:00:00 2001
From: Jordan Brough <jordan@animoto.com>
Date: Tue, 9 Feb 2010 13:50:35 -0700
Subject: [PATCH 2/2] Handling for db-enforced unique constraints in bang methods

---
 .../lib/active_record/unique_constraints.rb        |   33 ++++++++++++++-----
 activerecord/test/cases/unique_constraints_test.rb |   30 ++++++++++++++++++
 2 files changed, 54 insertions(+), 9 deletions(-)

diff --git a/activerecord/lib/active_record/unique_constraints.rb b/activerecord/lib/active_record/unique_constraints.rb
index 4a6d748..cb7a665 100644
--- a/activerecord/lib/active_record/unique_constraints.rb
+++ b/activerecord/lib/active_record/unique_constraints.rb
@@ -3,7 +3,9 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      alias_method_chain :save, :unique_constraints
+      [:save, :save!].each do |method|
+        alias_method_chain method, :unique_constraints
+      end
     end
 
     # work around postgres not allowing us to query indexes in the middle of an aborted transaction
@@ -15,15 +17,28 @@ module ActiveRecord
       cache_indexes
       save_without_unique_constraints(*args)
     rescue ActiveRecord::RecordNotUnique => e
-      index = connection.index_for_record_not_unique(e, self.class.table_name)
-      if !index
-        errors[:base] << I18n.t(:'activerecord.errors.messages.taken_generic')
-      elsif index.columns.size == 1
-        errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
-      else
-        errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
-      end
+      parse_unique_exception(e)
       false
     end
+
+    def save_with_unique_constraints! #:nodoc:
+      cache_indexes
+      save_without_unique_constraints!
+    rescue ActiveRecord::RecordNotUnique => e
+      parse_unique_exception(e)
+      raise RecordInvalid.new(self)
+    end
+
+    protected
+      def parse_unique_exception(e)
+        index = connection.index_for_record_not_unique(e, self.class.table_name)
+        if !index
+          errors[:base] << I18n.translate(:'activerecord.errors.messages.taken_generic')
+        elsif index.columns.size == 1
+          errors.add(index.columns.first, :taken, :value => attributes[index.columns.first])
+        else
+          errors.add(index.columns.first, :taken_multiple, :context => index.columns.slice(1..-1).join('/'), :value => attributes[index.columns.first])
+        end
+      end
   end
 end
diff --git a/activerecord/test/cases/unique_constraints_test.rb b/activerecord/test/cases/unique_constraints_test.rb
index 18d1890..d4489fc 100644
--- a/activerecord/test/cases/unique_constraints_test.rb
+++ b/activerecord/test/cases/unique_constraints_test.rb
@@ -9,6 +9,12 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal ["has already been taken"], invalid_item.errors[:uniq]
   end
 
+  def test_validate_uniqueness_on_create!
+    valid_item = UniqueItem.create!(:uniq => 'abc')
+    e = get_unique_exception { UniqueItem.create!(:uniq => 'abc') }
+    assert_equal ["has already been taken"], e.record.errors[:uniq]
+  end
+
   def test_validate_uniqueness_on_save
     item_1 = UniqueItem.create!(:uniq => 'abc')
     item_2 = UniqueItem.create!(:uniq => 'xyz')
@@ -17,6 +23,14 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal ["has already been taken"], item_2.errors[:uniq]
   end
 
+  def test_validate_uniqueness_on_save!
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    item_2.uniq = item_1.uniq
+    e = get_unique_exception { item_2.save! }
+    assert_equal(["has already been taken"], e.record.errors[:uniq])
+  end
+
   def test_validate_uniqueness_on_update
     item_1 = UniqueItem.create!(:uniq => 'abc')
     item_2 = UniqueItem.create!(:uniq => 'xyz')
@@ -24,6 +38,13 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal ["has already been taken"], item_2.errors[:uniq]
   end
 
+  def test_validate_uniqueness_on_update!
+    item_1 = UniqueItem.create!(:uniq => 'abc')
+    item_2 = UniqueItem.create!(:uniq => 'xyz')
+    e = get_unique_exception { item_2.update_attributes!(:uniq => item_1.uniq) }
+    assert_equal(["has already been taken"], e.record.errors[:uniq])
+  end
+
   def test_validate_uniqueness_multiple
     valid_item = UniqueItem.create!(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
     invalid_item = UniqueItem.create(:uniq_1 => 'a', :uniq_2 => 'b', :uniq_3 => 'c')
@@ -37,4 +58,13 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert_equal ["Unique requirement not met"], invalid_item.errors[:base]
   end
 
+  protected
+    def get_unique_exception
+      yield
+    rescue ActiveRecord::RecordInvalid => e
+      e
+    else
+      flunk "Expected ActiveRecord::RecordInvalid exception"
+    end
+
 end
-- 
1.7.2.1