Rails Lighthouse ticket #4347

foreign_keys-2.diff

From ef0c4e8af82f7c49c6b10c5b4d3cfb5021d90133 Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Wed, 7 Apr 2010 23:13:21 -0700
Subject: [PATCH 1/5] implementation without tests

---
 .../abstract/schema_definitions.rb                 |   31 +++++++
 .../abstract/schema_statements.rb                  |   88 ++++++++++++++++++++
 .../connection_adapters/mysql_adapter.rb           |   29 +++++++
 .../connection_adapters/postgresql_adapter.rb      |   48 +++++++++--
 .../connection_adapters/sqlite_adapter.rb          |   10 ++
 activerecord/lib/active_record/schema_dumper.rb    |   35 +++++++-
 6 files changed, 233 insertions(+), 8 deletions(-)

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 6c477e4..4d29fdc 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -261,6 +261,9 @@ module ActiveRecord
     class IndexDefinition < Struct.new(:table, :name, :unique, :columns) #:nodoc:
     end
 
+    class ForeignKeyDefinition < Struct.new(:referencing_table, :referenced_table, :options) #:nodoc:
+    end
+
     # Abstract representation of a column definition. Instances of this type
     # are typically created by methods in TableDefinition, and added to the
     # +columns+ attribute of said TableDefinition object, in order to be used
@@ -596,6 +599,21 @@ module ActiveRecord
         @base.add_index(@table_name, column_name, options)
       end
 
+      # Adds a new foreign key to the table. See SchemaStatements#add_foreign_key
+      #
+      # ===== Examples
+      # ====== Creating a simple foreign key
+      #  t.foreign_key(:people)
+      # ====== Defining the column
+      #  t.foreign_key(:people, :column => :sender_id)
+      # ====== Creating a named foreign key
+      #  t.foreign_key(:people, :column => :sender_id, :name => 'sender_foreign_key')
+      # ====== Cascade delete this table if referenced_table is deleted.
+      #  t.foreign_key(:people, :column => :sender_id, :dependency => :delete)
+      def foreign_key(referenced_table, options = {})
+        @base.add_foreign_key(@table_name, referenced_table, options)
+      end
+
       # Adds timestamps (created_at and updated_at) columns to the table. See SchemaStatements#add_timestamps
       # ===== Example
       #  t.timestamps
@@ -643,6 +661,19 @@ module ActiveRecord
         @base.remove_index(@table_name, options)
       end
 
+      # Remove the given foreign key from the table.
+      #
+      # ===== Examples
+      # ====== Remove the fk_suppliers_company_id in the suppliers table.
+      #   t.remove_foreign_key :companies
+      # ====== Remove the foreign key named fk_accounts_branch_id in the accounts table.
+      #   remove_foreign_key :column => :branch_id
+      # ====== Remove the foreign key named party_foreign_key in the accounts table.
+      #   remove_index :name => :party_foreign_key
+      def remove_foreign_key(referenced_table_or_options)
+        @base.remove_foreign_key(@table_name, referenced_table_or_options)
+      end
+
       # Removes the timestamp columns (created_at and updated_at) from the table.
       # ===== Example
       #  t.remove_timestamps
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 6d4ab50..745e386 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -308,6 +308,94 @@ module ActiveRecord
         end
       end
 
+      # Adds a new foreign key to the +referencing_table+, pointing to the primary key of the +referenced_table+
+      #
+      # The foreign key will be named after the +referencing_table+ and column, unless you pass
+      # <tt>:name</tt> as an option.
+      #
+      # ===== Examples
+      # ====== Creating a foreign key
+      #  add_foreign_key(:comments, :posts)
+      # generates
+      #  ALTER TABLE `comments` ADD CONSTRAINT
+      #     `fk_comments_post_id` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`)
+      # 
+      # ====== Creating a named foreign key
+      #  add_foreign_key(:comments, :posts, :name => 'comments_belongs_to_posts')
+      # generates
+      #  ALTER TABLE `comments` ADD CONSTRAINT
+      #     `comments_belongs_to_posts` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`)
+      # 
+      # ====== Creating a cascading foreign_key on a custom column
+      #  add_foreign_key(:people, :people, :column => 'best_friend_id', :dependent => :nullify)
+      # generates
+      #  ALTER TABLE `people` ADD CONSTRAINT
+      #     `fk_people_best_friend_id` FOREIGN KEY (`best_friend_id`) REFERENCES `people` (`id`)
+      #     ON DELETE SET NULL
+      # 
+      # === Supported options
+      # [:column]
+      #   Specify the column name on the referencing_table that points to the referenced_table. By default
+      #   this is guessed to be the singular name of the referenced_table with "_id" suffixed. So a referenced_table
+      #   of :posts will use "post_id" as the default <tt>:column</tt>.
+      # [:name]
+      #   Specify the name of the foreign key constraint. This defaults to use the referencing_table and column.
+      # [:primary_key]
+      #   Specify the column name on the referenced_table that is referenced by this foreign key. This defaults to "id".
+      # [:dependent]
+      #   If set to <tt>:delete</tt>, the associated records in the referencing_table are deleted when records
+      #   in referenced_table are deleted. If set to <tt>:nullify</tt>, the foreign key column is set to +NULL+.
+      def add_foreign_key(referencing_table, referenced_table, options = {})
+        column            = options[:column] || "#{referenced_table.to_s.singularize}_id"
+        foreign_key_name  = foreign_key_name(referencing_table, options.merge(:column => column))
+        primary_key       = options[:primary_key] || 'id'
+        dependency        = foreign_key_dependency(options)
+
+        execute(
+          "ALTER TABLE #{quote_table_name(referencing_table)} " +
+          "ADD CONSTRAINT #{quote_column_name(foreign_key_name)} " +
+          "FOREIGN KEY (#{quote_column_name(column)}) " +
+          "REFERENCES #{quote_table_name(ActiveRecord::Migrator.proper_table_name(referenced_table))}(#{primary_key}) " +
+          dependency
+        )
+      end
+
+      # Remove the given foreign key from the table.
+      #
+      # Remove the foreign key fk_suppliers_company_id in the suppliers table.
+      #   remove_foreign_key :suppliers, :companies
+      # Remove the foreign key fk_accounts_branch_id in the accounts table.
+      #   remove_foreign_key :accounts, :column => :branch_id
+      # Remove the foreign key named party_foreign_key in the accounts table.
+      #   remove_foreign_key :accounts, :name => :party_foreign_key
+      def remove_foreign_key(referencing_table, referenced_table_or_options)
+        if Hash === options
+          foreign_key_name = foreign_key_name(referencing_table, options)
+        else
+          foreign_key_name = foreign_key_name(referencing_table, :column => "#{referenced_table.to_s.singularize}_id")
+        end
+
+        execute "ALTER TABLE #{quote_table_name(referencing_table)} DROP FOREIGN KEY #{quote_column_name(foreign_key_name)}"
+      end
+
+      def foreign_key_name(referencing_table, options)
+        if options[:name]
+          options[:name]
+        elsif options[:column]
+          "fk_#{referencing_table}_#{options[:column]}"
+        else
+          raise ArgumentError, "You must specify the foreign key name"
+        end
+      end
+
+      def foreign_key_dependency(options)
+        case options[:dependency]
+          when :nullify then "ON DELETE SET NULL"
+          when :delete  then "ON DELETE CASCADE"
+          else ""
+        end
+      end
+
       # Returns a string of <tt>CREATE TABLE</tt> SQL statement(s) for recreating the
       # entire structure of the database.
       def structure_dump
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 55d9d20..1076a40 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -469,6 +469,35 @@ module ActiveRecord
         result.free
         indexes
       end
+      
+      def foreign_keys(table_name, name = nil)#:nodoc:
+        results = select_all(<<-SQL, name)
+          SELECT fk.referenced_table_name as 'referenced_table'
+                ,fk.referenced_column_name as 'primary_key'
+                ,fk.column_name as 'column'
+                ,fk.constraint_name as 'name'
+          FROM information_schema.key_column_usage fk
+          WHERE fk.referenced_column_name is not null
+            AND fk.table_schema = '#{@config[:database]}'
+            AND fk.table_name = '#{table_name}'
+        SQL
+
+        structure = select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
+
+        results.map do |row|
+          options = {:column => row['column'], :name => row['name'], :primary_key => row['primary_key']}
+
+          if structure =~ /CONSTRAINT #{quote_column_name(row['name'])} FOREIGN KEY .* REFERENCES .* ON DELETE (CASCADE|SET NULL)/
+            if $1 == 'CASCADE'
+              options[:dependent] = :delete
+            elsif $1 == 'SET NULL'
+              options[:dependent] = :nullify
+            end
+          end
+
+          ForeignKeyDefinition.new(table_name, row['referenced_table'], options)
+        end
+      end
 
       def columns(table_name, name = nil)#:nodoc:
         sql = "SHOW FIELDS FROM #{quote_table_name(table_name)}"
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 2395a74..491c4c3 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -703,10 +703,7 @@ module ActiveRecord
           ORDER BY i.relname
         SQL
 
-
-        indexes = []
-
-        indexes = result.map do |row|
+        result.map do |row|
           index_name = row[0]
           unique = row[1] == 't'
           indkey = row[2].split(" ")
@@ -721,10 +718,39 @@ module ActiveRecord
 
           column_names = indkey.map {|attnum| columns[attnum] }
           IndexDefinition.new(table_name, index_name, unique, column_names)
-
         end
+      end
 
-        indexes
+      def foreign_keys(table_name, name = nil)
+        results = select_all(<<-SQL, name)
+          SELECT tc.constraint_name as name
+                ,ccu.table_name as referenced_table
+                ,ccu.column_name as primary_key
+                ,kcu.column_name as column
+                ,rc.delete_rule as dependency
+          FROM information_schema.table_constraints tc
+          JOIN information_schema.key_column_usage kcu
+          USING (constraint_catalog, constraint_schema, constraint_name)
+          JOIN information_schema.referential_constraints rc
+          USING (constraint_catalog, constraint_schema, constraint_name)
+          JOIN information_schema.constraint_column_usage ccu
+          USING (constraint_catalog, constraint_schema, constraint_name)
+          WHERE tc.constraint_type = 'FOREIGN KEY'
+            AND tc.constraint_catalog = '#{@config[:database]}'
+            AND tc.table_name = '#{table_name}'
+        SQL
+
+        results.map do |row|
+          options = {:column => row['column'], :name => row['name'], :primary_key => row['primary_key']}
+
+          if row['dependency'] == 'CASCADE'
+            options[:dependent] = :delete
+          elsif row['dependency'] == 'SET NULL'
+            options[:dependent] = :nullify
+          end
+
+          ForeignKeyDefinition.new(table_name, row['referenced_table'], options)
+        end
       end
 
       # Returns the list of all column definitions for a table.
@@ -922,6 +948,16 @@ module ActiveRecord
         execute "DROP INDEX #{quote_table_name(index_name(table_name, options))}"
       end
 
+      def remove_foreign_key(table, options)
+        if Hash === options
+          foreign_key_name = foreign_key_name(table, options[:column], options)
+        else
+          foreign_key_name = foreign_key_name(table, "#{options.to_s.singularize}_id")
+        end
+
+        execute "ALTER TABLE #{quote_table_name(table)} DROP CONSTRAINT #{quote_column_name(foreign_key_name)}"
+      end
+
       # Maps logical Rails types to PostgreSQL-specific data types.
       def type_to_sql(type, limit = nil, precision = nil, scale = nil)
         return super unless type.to_s == 'integer'
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 29225b8..09ead91 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -211,6 +211,10 @@ module ActiveRecord
           index
         end
       end
+      
+      def foreign_keys(table_name, name = nil)
+        []
+      end
 
       def primary_key(table_name) #:nodoc:
         column = table_structure(table_name).find {|field| field['pk'].to_i == 1}
@@ -221,6 +225,12 @@ module ActiveRecord
         execute "DROP INDEX #{quote_column_name(index_name(table_name, options))}"
       end
 
+      def add_foreign_key(referencing_table, referenced_table, options = {})
+      end
+
+      def remove_foreign_key(referencing_table, referenced_table_or_options)
+      end
+
       def rename_table(name, new_name)
         execute "ALTER TABLE #{quote_table_name(name)} RENAME TO #{quote_table_name(new_name)}"
       end
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index c8e1b4f..6bbe934 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -6,7 +6,7 @@ module ActiveRecord
   # output format (i.e., ActiveRecord::Schema).
   class SchemaDumper #:nodoc:
     private_class_method :new
-    
+
     ##
     # :singleton-method:
     # A list of tables which should not be dumped to the schema. 
@@ -38,7 +38,7 @@ module ActiveRecord
       def header(stream)
         define_params = @version ? ":version => #{@version}" : ""
 
-        stream.puts <<HEADER
+        stream.puts <<-HEADER
 # This file is auto-generated from the current state of the database. Instead of editing this file, 
 # please use the migrations feature of Active Record to incrementally modify your database, and
 # then regenerate this schema definition.
@@ -60,6 +60,8 @@ HEADER
       end
 
       def tables(stream)
+        fks = StringIO.new
+
         @connection.tables.sort.each do |tbl|
           next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|
             case ignored
@@ -70,7 +72,11 @@ HEADER
             end
           end 
           table(tbl, stream)
+          foreign_keys(tbl, fks)
         end
+
+        fks.rewind
+        stream.print fks.read
       end
 
       def table(table, stream)
@@ -185,5 +191,30 @@ HEADER
           stream.puts
         end
       end
+
+      def foreign_keys(table_name, stream)
+        if (foreign_keys = @connection.foreign_keys(table_name)).any?
+          add_foreign_key_statements = foreign_keys.map do |foreign_key|
+            statement_parts = [ ('add_foreign_key ' + foreign_key.referencing_table.inspect) ]
+            statement_parts << foreign_key.referenced_table.inspect
+            statement_parts << (':name => ' + foreign_key.options[:name].inspect)
+            
+            if foreign_key.options[:column] != "#{foreign_key.referenced_table.singularize}_id"
+              statement_parts << (':column => ' + foreign_key.options[:column].inspect)
+            end
+            if foreign_key.options[:primary_key] != 'id'
+              statement_parts << (':primary_key => ' + foreign_key.options[:primary_key].inspect)
+            end
+            if foreign_key.options[:dependent].present?
+              statement_parts << (':dependent => ' + foreign_key.options[:dependent].inspect)
+            end
+
+            '  ' + statement_parts.join(', ')
+          end
+
+          stream.puts add_foreign_key_statements.sort.join("\n")
+          stream.puts
+        end
+      end
   end
 end
-- 
1.7.0.4


From 6e9ab8df9e7c5aae36bf66e7970e730385d6ca59 Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 09:54:46 -0700
Subject: [PATCH 2/5] Tests, tweaks and docs

---
 .../abstract/schema_statements.rb                  |    6 ++--
 .../connection_adapters/abstract_adapter.rb        |    6 +++++
 .../connection_adapters/sqlite_adapter.rb          |    4 +++
 activerecord/lib/active_record/migration.rb        |    3 ++
 activerecord/test/cases/adapter_test.rb            |   24 ++++++++++++++++++-
 activerecord/test/cases/migration_test.rb          |   18 +++++++++++++++
 activerecord/test/cases/schema_dumper_test.rb      |    4 +++
 activerecord/test/schema/schema.rb                 |   24 +++++--------------
 railties/guides/source/migrations.textile          |    4 ++-
 9 files changed, 70 insertions(+), 23 deletions(-)

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 745e386..b2ac01d 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -368,11 +368,11 @@ module ActiveRecord
       #   remove_foreign_key :accounts, :column => :branch_id
       # Remove the foreign key named party_foreign_key in the accounts table.
       #   remove_foreign_key :accounts, :name => :party_foreign_key
-      def remove_foreign_key(referencing_table, referenced_table_or_options)
+      def remove_foreign_key(referencing_table, options)
         if Hash === options
           foreign_key_name = foreign_key_name(referencing_table, options)
         else
-          foreign_key_name = foreign_key_name(referencing_table, :column => "#{referenced_table.to_s.singularize}_id")
+          foreign_key_name = foreign_key_name(referencing_table, :column => "#{options.to_s.singularize}_id")
         end
 
         execute "ALTER TABLE #{quote_table_name(referencing_table)} DROP FOREIGN KEY #{quote_column_name(foreign_key_name)}"
@@ -389,7 +389,7 @@ module ActiveRecord
       end
 
       def foreign_key_dependency(options)
-        case options[:dependency]
+        case options[:dependent]
           when :nullify then "ON DELETE SET NULL"
           when :delete  then "ON DELETE CASCADE"
           else ""
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 6ffffc8..9ea3801 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -62,6 +62,12 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support foreign key constraints?  This is +true+
+      # for all adapters except sqlite.
+      def supports_foreign_keys?
+        true
+      end
+
       # Does this adapter support using DISTINCT within COUNT?  This is +true+
       # for all adapters except sqlite.
       def supports_count_distinct?
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 09ead91..b002e86 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -84,6 +84,10 @@ module ActiveRecord
         true
       end
 
+      def supports_foreign_keys?
+        false
+      end
+
       def requires_reloading?
         true
       end
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index c163fb9..d96de14 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -96,6 +96,9 @@ module ActiveRecord
   # * <tt>add_index(table_name, column_names, options)</tt>: Adds a new index with the name of the column. Other options include
   #   <tt>:name</tt> and <tt>:unique</tt> (e.g. <tt>{ :name => "users_name_index", :unique => true }</tt>).
   # * <tt>remove_index(table_name, index_name)</tt>: Removes the index specified by +index_name+.
+  # * <tt>add_foreign_key(referencing_table, referenced_table, options)</tt>: Adds a new foreign key to the referencing_table,
+  #   with a constraint on the primary key of the referenced_table. Options include <tt>:column</tt>, <tt>:name</tt>, <tt>:primary_key</tt>
+  #   and <tt>:dependent</tt>. (e.g. <tt>{:name => 'my_foreign_key', :column => 'author_id', :dependent => :delete})
   #
   # == Irreversible transformations
   #
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 9f78ae0..f8ff892 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -41,6 +41,26 @@ class AdapterTest < ActiveRecord::TestCase
     @connection.remove_index(:accounts, :name => idx_name) rescue nil
   end
 
+  def test_foreign_keys
+    fk_name = 'favorited_author'
+
+    if @connection.supports_foreign_keys?
+      foreign_keys = @connection.foreign_keys("author_favorites")
+      assert foreign_keys.empty?
+
+      @connection.add_foreign_key :author_favorites, :authors, :name => fk_name, :column => 'favorite_author_id', :dependent => :delete
+      @connection.foreign_keys("author_favorites").first.tap do |foreign_key|
+        assert_equal 'author_favorites', foreign_key.referencing_table
+        assert_equal 'authors', foreign_key.referenced_table
+        assert_equal fk_name, foreign_key.options[:name]
+        assert_equal 'favorite_author_id', foreign_key.options[:column]
+        assert_equal :delete, foreign_key.options[:dependent]
+      end
+    end
+  ensure
+    @connection.remove_foreign_key :author_favorites, :name => fk_name
+  end
+
   def test_current_database
     if @connection.respond_to?(:current_database)
       assert_equal ENV['ARUNIT_DB_NAME'] || "activerecord_unittest", @connection.current_database
@@ -136,7 +156,7 @@ class AdapterTest < ActiveRecord::TestCase
   end
 
   def test_foreign_key_violations_are_translated_to_specific_exception
-    unless @connection.adapter_name == 'SQLite'
+    if @connection.supports_foreign_keys?
       assert_raises(ActiveRecord::InvalidForeignKey) do
         # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
         if @connection.prefetch_primary_key?
@@ -151,7 +171,7 @@ class AdapterTest < ActiveRecord::TestCase
 
   def test_add_limit_offset_should_sanitize_sql_injection_for_limit_without_comas
     sql_inject = "1 select * from schema"
-      assert_equal " LIMIT 1", @connection.add_limit_offset!("", :limit => sql_inject)
+    assert_equal " LIMIT 1", @connection.add_limit_offset!("", :limit => sql_inject)
     if current_adapter?(:MysqlAdapter)
       assert_equal " LIMIT 7, 1", @connection.add_limit_offset!("", :limit => sql_inject, :offset => 7)
     else
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index e213986..67a464e 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -111,6 +111,17 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_add_foreign_key
+      Subscription.delete_all
+      Order.delete_all
+      assert_nothing_raised { Subscription.connection.add_foreign_key :subscriptions, :books }
+      assert_nothing_raised { Subscription.connection.remove_foreign_key :subscriptions, :books }
+      assert_nothing_raised { Subscription.connection.add_foreign_key :subscriptions, :books, :name => 'fk_subscribed_books' }
+      assert_nothing_raised { Subscription.connection.remove_foreign_key :subscriptions, :name => 'fk_subscribed_books' }
+      assert_nothing_raised { Order.connection.add_foreign_key :orders, :people, :column => 'billing_customer_id'}
+      assert_nothing_raised { Order.connection.remove_foreign_key :orders, :column => 'billing_customer_id' }
+    end
+
     def testing_table_with_only_foo_attribute
       Person.connection.create_table :testings, :id => false do |t|
         t.column :foo, :string
@@ -1606,6 +1617,13 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_foreign_key_creates_foreign_key
+      with_change_table do |t|
+        @connection.expects(:add_foreign_key).with(:delete_me, :bar, {:dependent => :delete})
+        t.foreign_key :bar, :dependent => :delete
+      end
+    end
+
     def test_change_changes_column
       with_change_table do |t|
         @connection.expects(:change_column).with(:delete_me, :bar, :string, {})
diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index 1c43e3c..3af5698 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -162,6 +162,10 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_equal 'add_index "companies", ["firm_id", "type", "rating", "ruby_type"], :name => "company_index"', index_definition
   end
 
+  def test_foreign_keys
+    output = standard_dump
+  end
+
   def test_schema_dump_should_honor_nonstandard_primary_keys
     output = standard_dump
     match = output.match(%r{create_table "movies"(.*)do})
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index bec4291..18698cf 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -1,10 +1,4 @@
 ActiveRecord::Schema.define do
-  def except(adapter_names_to_exclude)
-    unless [adapter_names_to_exclude].flatten.include?(adapter_name)
-      yield
-    end
-  end
-
   #put adapter specific setup here
   case adapter_name
     # For Firebird, set the sequence values 10000 when create_table is called;
@@ -545,18 +539,14 @@ ActiveRecord::Schema.define do
   create_table :zines, :force => true do |t|
     t.string :title
   end
-
-  except 'SQLite' do
-    # fk_test_has_fk should be before fk_test_has_pk
-    create_table :fk_test_has_fk, :force => true do |t|
-      t.integer :fk_id, :null => false
-    end
-
-    create_table :fk_test_has_pk, :force => true do |t|
-    end
-
-    execute "ALTER TABLE fk_test_has_fk ADD CONSTRAINT fk_name FOREIGN KEY (#{quote_column_name 'fk_id'}) REFERENCES #{quote_table_name 'fk_test_has_pk'} (#{quote_column_name 'id'})"
+  
+  create_table :fk_test_has_fk, :force => true do |t|
+    t.integer :fk_id, :null => false
+  end
+  
+  create_table :fk_test_has_pk, :force => true do |t|
   end
+  add_foreign_key :fk_test_has_fk, :fk_test_has_pk, :column => :fk_id, :name => 'fk_id'
 end
 
 Course.connection.create_table :courses, :force => true do |t|
diff --git a/railties/guides/source/migrations.textile b/railties/guides/source/migrations.textile
index 558cbb4..c3fca91 100644
--- a/railties/guides/source/migrations.textile
+++ b/railties/guides/source/migrations.textile
@@ -75,6 +75,8 @@ Active Record provides methods that perform common data definition tasks in a da
 * +remove_column+
 * +add_index+
 * +remove_index+
+* +add_foreign_key+
+* +remove_foreign_key+
 
 If you need to perform tasks specific to your database (for example create a "foreign key":#active-record-and-referential-integrity constraint) then the +execute+ function allows you to execute arbitrary SQL. A migration is just a regular Ruby class so you're not limited to these functions. For example after adding a column you could write code to set the value of that column for existing records (if necessary using your models).
 
@@ -564,7 +566,7 @@ ActiveRecord::Schema.define(:version => 20080906171750) do
 end
 </ruby>
 
-In many ways this is exactly what it is. This file is created by inspecting the database and expressing its structure using +create_table+, +add_index+, and so on. Because this is database independent it could be loaded into any database that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases.
+In many ways this is exactly what it is. This file is created by inspecting the database and expressing its structure using +create_table+, +add_index+, and +add_foreign_key+. Because this is database independent it could be loaded into any database that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases.
 
 There is however a trade-off: +db/schema.rb+ cannot express database specific items such as foreign key constraints, triggers or stored procedures. While in a migration you can execute custom SQL statements, the schema dumper cannot reconstitute those statements from the database. If you are using features like this then you should set the schema format to +:sql+.
 
-- 
1.7.0.4


From e6cff6d8ce35e6bd9a85b17a24859621f31e6e7d Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 10:02:18 -0700
Subject: [PATCH 3/5] Add test for t.remove_foreign_key

---
 activerecord/test/cases/migration_test.rb |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index 67a464e..d64ecc8 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -1,7 +1,9 @@
 require "cases/helper"
 require 'bigdecimal/util'
 
+require 'models/order'
 require 'models/person'
+require 'models/subscription'
 require 'models/topic'
 require 'models/developer'
 
@@ -1666,6 +1668,13 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_remove_foreign_key
+      with_change_table do |t|
+        @connection.expects(:remove_foreign_key).with(:delete_me, {:name => 'foo'})
+        t.remove_foreign_key :name => 'foo'
+      end
+    end
+
     def test_rename_renames_column
       with_change_table do |t|
         @connection.expects(:rename_column).with(:delete_me, :bar, :baz)
-- 
1.7.0.4


From ea44ccd6872f19fea7489ba383ce446ade27dcce Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 10:29:30 -0700
Subject: [PATCH 4/5] Separate table dumps from foreign key dumps

---
 activerecord/lib/active_record/schema_dumper.rb |   18 ++++++------------
 1 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index 6bbe934..6e206c6 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -22,7 +22,8 @@ module ActiveRecord
 
     def dump(stream)
       header(stream)
-      tables(stream)
+      table_names.each { |tbl| table(tbl, stream) }
+      table_names.each { |tbl| foreign_keys(tbl, stream) }
       trailer(stream)
       stream
     end
@@ -59,24 +60,17 @@ HEADER
         stream.puts "end"
       end
 
-      def tables(stream)
-        fks = StringIO.new
-
-        @connection.tables.sort.each do |tbl|
-          next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|
+      def table_names
+        @connection.tables.sort.reject do |tbl|
+          ['schema_migrations', ignore_tables].flatten.any? do |ignored|
             case ignored
             when String; tbl == ignored
             when Regexp; tbl =~ ignored
             else
               raise StandardError, 'ActiveRecord::SchemaDumper.ignore_tables accepts an array of String and / or Regexp values.'
             end
-          end 
-          table(tbl, stream)
-          foreign_keys(tbl, fks)
+          end
         end
-
-        fks.rewind
-        stream.print fks.read
       end
 
       def table(table, stream)
-- 
1.7.0.4


From e96b4e5e5e3f240168f988f0afcfb6886a18d2eb Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 13:44:05 -0700
Subject: [PATCH 5/5] Complete foreign key tests in schema_dumper

---
 activerecord/test/cases/schema_dumper_test.rb |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index 3af5698..027d30b 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -162,8 +162,12 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_equal 'add_index "companies", ["firm_id", "type", "rating", "ruby_type"], :name => "company_index"', index_definition
   end
 
-  def test_foreign_keys
-    output = standard_dump
+  def test_foreign_keys_dumped_after_tables
+    if ActiveRecord::Base.connection.supports_foreign_keys?
+      output = standard_dump
+      assert_match %r{create_table(.|\n)*add_foreign_key}, output
+      assert_no_match %r{add_foreign_key(.|\n)*create_table}, output
+    end
   end
 
   def test_schema_dump_should_honor_nonstandard_primary_keys
-- 
1.7.0.4

foreign_keys.diff

From ab18f1b0f58ee9e154179c75462a438404ea4fe0 Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Wed, 7 Apr 2010 23:13:21 -0700
Subject: [PATCH 1/4] implementation without tests

---
 .../abstract/schema_definitions.rb                 |   31 +++++++
 .../abstract/schema_statements.rb                  |   88 ++++++++++++++++++++
 .../connection_adapters/mysql_adapter.rb           |   29 +++++++
 .../connection_adapters/postgresql_adapter.rb      |   48 +++++++++--
 .../connection_adapters/sqlite_adapter.rb          |   10 ++
 activerecord/lib/active_record/schema_dumper.rb    |   35 +++++++-
 6 files changed, 233 insertions(+), 8 deletions(-)

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 6c477e4..4d29fdc 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -261,6 +261,9 @@ module ActiveRecord
     class IndexDefinition < Struct.new(:table, :name, :unique, :columns) #:nodoc:
     end
 
+    class ForeignKeyDefinition < Struct.new(:referencing_table, :referenced_table, :options) #:nodoc:
+    end
+
     # Abstract representation of a column definition. Instances of this type
     # are typically created by methods in TableDefinition, and added to the
     # +columns+ attribute of said TableDefinition object, in order to be used
@@ -596,6 +599,21 @@ module ActiveRecord
         @base.add_index(@table_name, column_name, options)
       end
 
+      # Adds a new foreign key to the table. See SchemaStatements#add_foreign_key
+      #
+      # ===== Examples
+      # ====== Creating a simple foreign key
+      #  t.foreign_key(:people)
+      # ====== Defining the column
+      #  t.foreign_key(:people, :column => :sender_id)
+      # ====== Creating a named foreign key
+      #  t.foreign_key(:people, :column => :sender_id, :name => 'sender_foreign_key')
+      # ====== Cascade delete this table if referenced_table is deleted.
+      #  t.foreign_key(:people, :column => :sender_id, :dependency => :delete)
+      def foreign_key(referenced_table, options = {})
+        @base.add_foreign_key(@table_name, referenced_table, options)
+      end
+
       # Adds timestamps (created_at and updated_at) columns to the table. See SchemaStatements#add_timestamps
       # ===== Example
       #  t.timestamps
@@ -643,6 +661,19 @@ module ActiveRecord
         @base.remove_index(@table_name, options)
       end
 
+      # Remove the given foreign key from the table.
+      #
+      # ===== Examples
+      # ====== Remove the fk_suppliers_company_id in the suppliers table.
+      #   t.remove_foreign_key :companies
+      # ====== Remove the foreign key named fk_accounts_branch_id in the accounts table.
+      #   remove_foreign_key :column => :branch_id
+      # ====== Remove the foreign key named party_foreign_key in the accounts table.
+      #   remove_index :name => :party_foreign_key
+      def remove_foreign_key(referenced_table_or_options)
+        @base.remove_foreign_key(@table_name, referenced_table_or_options)
+      end
+
       # Removes the timestamp columns (created_at and updated_at) from the table.
       # ===== Example
       #  t.remove_timestamps
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 6d4ab50..745e386 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -308,6 +308,94 @@ module ActiveRecord
         end
       end
 
+      # Adds a new foreign key to the +referencing_table+, pointing to the primary key of the +referenced_table+
+      #
+      # The foreign key will be named after the +referencing_table+ and column, unless you pass
+      # <tt>:name</tt> as an option.
+      #
+      # ===== Examples
+      # ====== Creating a foreign key
+      #  add_foreign_key(:comments, :posts)
+      # generates
+      #  ALTER TABLE `comments` ADD CONSTRAINT
+      #     `fk_comments_post_id` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`)
+      # 
+      # ====== Creating a named foreign key
+      #  add_foreign_key(:comments, :posts, :name => 'comments_belongs_to_posts')
+      # generates
+      #  ALTER TABLE `comments` ADD CONSTRAINT
+      #     `comments_belongs_to_posts` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`)
+      # 
+      # ====== Creating a cascading foreign_key on a custom column
+      #  add_foreign_key(:people, :people, :column => 'best_friend_id', :dependent => :nullify)
+      # generates
+      #  ALTER TABLE `people` ADD CONSTRAINT
+      #     `fk_people_best_friend_id` FOREIGN KEY (`best_friend_id`) REFERENCES `people` (`id`)
+      #     ON DELETE SET NULL
+      # 
+      # === Supported options
+      # [:column]
+      #   Specify the column name on the referencing_table that points to the referenced_table. By default
+      #   this is guessed to be the singular name of the referenced_table with "_id" suffixed. So a referenced_table
+      #   of :posts will use "post_id" as the default <tt>:column</tt>.
+      # [:name]
+      #   Specify the name of the foreign key constraint. This defaults to use the referencing_table and column.
+      # [:primary_key]
+      #   Specify the column name on the referenced_table that is referenced by this foreign key. This defaults to "id".
+      # [:dependent]
+      #   If set to <tt>:delete</tt>, the associated records in the referencing_table are deleted when records
+      #   in referenced_table are deleted. If set to <tt>:nullify</tt>, the foreign key column is set to +NULL+.
+      def add_foreign_key(referencing_table, referenced_table, options = {})
+        column            = options[:column] || "#{referenced_table.to_s.singularize}_id"
+        foreign_key_name  = foreign_key_name(referencing_table, options.merge(:column => column))
+        primary_key       = options[:primary_key] || 'id'
+        dependency        = foreign_key_dependency(options)
+
+        execute(
+          "ALTER TABLE #{quote_table_name(referencing_table)} " +
+          "ADD CONSTRAINT #{quote_column_name(foreign_key_name)} " +
+          "FOREIGN KEY (#{quote_column_name(column)}) " +
+          "REFERENCES #{quote_table_name(ActiveRecord::Migrator.proper_table_name(referenced_table))}(#{primary_key}) " +
+          dependency
+        )
+      end
+
+      # Remove the given foreign key from the table.
+      #
+      # Remove the foreign key fk_suppliers_company_id in the suppliers table.
+      #   remove_foreign_key :suppliers, :companies
+      # Remove the foreign key fk_accounts_branch_id in the accounts table.
+      #   remove_foreign_key :accounts, :column => :branch_id
+      # Remove the foreign key named party_foreign_key in the accounts table.
+      #   remove_foreign_key :accounts, :name => :party_foreign_key
+      def remove_foreign_key(referencing_table, referenced_table_or_options)
+        if Hash === options
+          foreign_key_name = foreign_key_name(referencing_table, options)
+        else
+          foreign_key_name = foreign_key_name(referencing_table, :column => "#{referenced_table.to_s.singularize}_id")
+        end
+
+        execute "ALTER TABLE #{quote_table_name(referencing_table)} DROP FOREIGN KEY #{quote_column_name(foreign_key_name)}"
+      end
+
+      def foreign_key_name(referencing_table, options)
+        if options[:name]
+          options[:name]
+        elsif options[:column]
+          "fk_#{referencing_table}_#{options[:column]}"
+        else
+          raise ArgumentError, "You must specify the foreign key name"
+        end
+      end
+
+      def foreign_key_dependency(options)
+        case options[:dependency]
+          when :nullify then "ON DELETE SET NULL"
+          when :delete  then "ON DELETE CASCADE"
+          else ""
+        end
+      end
+
       # Returns a string of <tt>CREATE TABLE</tt> SQL statement(s) for recreating the
       # entire structure of the database.
       def structure_dump
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index 55d9d20..1076a40 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -469,6 +469,35 @@ module ActiveRecord
         result.free
         indexes
       end
+      
+      def foreign_keys(table_name, name = nil)#:nodoc:
+        results = select_all(<<-SQL, name)
+          SELECT fk.referenced_table_name as 'referenced_table'
+                ,fk.referenced_column_name as 'primary_key'
+                ,fk.column_name as 'column'
+                ,fk.constraint_name as 'name'
+          FROM information_schema.key_column_usage fk
+          WHERE fk.referenced_column_name is not null
+            AND fk.table_schema = '#{@config[:database]}'
+            AND fk.table_name = '#{table_name}'
+        SQL
+
+        structure = select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
+
+        results.map do |row|
+          options = {:column => row['column'], :name => row['name'], :primary_key => row['primary_key']}
+
+          if structure =~ /CONSTRAINT #{quote_column_name(row['name'])} FOREIGN KEY .* REFERENCES .* ON DELETE (CASCADE|SET NULL)/
+            if $1 == 'CASCADE'
+              options[:dependent] = :delete
+            elsif $1 == 'SET NULL'
+              options[:dependent] = :nullify
+            end
+          end
+
+          ForeignKeyDefinition.new(table_name, row['referenced_table'], options)
+        end
+      end
 
       def columns(table_name, name = nil)#:nodoc:
         sql = "SHOW FIELDS FROM #{quote_table_name(table_name)}"
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 2395a74..491c4c3 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -703,10 +703,7 @@ module ActiveRecord
           ORDER BY i.relname
         SQL
 
-
-        indexes = []
-
-        indexes = result.map do |row|
+        result.map do |row|
           index_name = row[0]
           unique = row[1] == 't'
           indkey = row[2].split(" ")
@@ -721,10 +718,39 @@ module ActiveRecord
 
           column_names = indkey.map {|attnum| columns[attnum] }
           IndexDefinition.new(table_name, index_name, unique, column_names)
-
         end
+      end
 
-        indexes
+      def foreign_keys(table_name, name = nil)
+        results = select_all(<<-SQL, name)
+          SELECT tc.constraint_name as name
+                ,ccu.table_name as referenced_table
+                ,ccu.column_name as primary_key
+                ,kcu.column_name as column
+                ,rc.delete_rule as dependency
+          FROM information_schema.table_constraints tc
+          JOIN information_schema.key_column_usage kcu
+          USING (constraint_catalog, constraint_schema, constraint_name)
+          JOIN information_schema.referential_constraints rc
+          USING (constraint_catalog, constraint_schema, constraint_name)
+          JOIN information_schema.constraint_column_usage ccu
+          USING (constraint_catalog, constraint_schema, constraint_name)
+          WHERE tc.constraint_type = 'FOREIGN KEY'
+            AND tc.constraint_catalog = '#{@config[:database]}'
+            AND tc.table_name = '#{table_name}'
+        SQL
+
+        results.map do |row|
+          options = {:column => row['column'], :name => row['name'], :primary_key => row['primary_key']}
+
+          if row['dependency'] == 'CASCADE'
+            options[:dependent] = :delete
+          elsif row['dependency'] == 'SET NULL'
+            options[:dependent] = :nullify
+          end
+
+          ForeignKeyDefinition.new(table_name, row['referenced_table'], options)
+        end
       end
 
       # Returns the list of all column definitions for a table.
@@ -922,6 +948,16 @@ module ActiveRecord
         execute "DROP INDEX #{quote_table_name(index_name(table_name, options))}"
       end
 
+      def remove_foreign_key(table, options)
+        if Hash === options
+          foreign_key_name = foreign_key_name(table, options[:column], options)
+        else
+          foreign_key_name = foreign_key_name(table, "#{options.to_s.singularize}_id")
+        end
+
+        execute "ALTER TABLE #{quote_table_name(table)} DROP CONSTRAINT #{quote_column_name(foreign_key_name)}"
+      end
+
       # Maps logical Rails types to PostgreSQL-specific data types.
       def type_to_sql(type, limit = nil, precision = nil, scale = nil)
         return super unless type.to_s == 'integer'
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 29225b8..09ead91 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -211,6 +211,10 @@ module ActiveRecord
           index
         end
       end
+      
+      def foreign_keys(table_name, name = nil)
+        []
+      end
 
       def primary_key(table_name) #:nodoc:
         column = table_structure(table_name).find {|field| field['pk'].to_i == 1}
@@ -221,6 +225,12 @@ module ActiveRecord
         execute "DROP INDEX #{quote_column_name(index_name(table_name, options))}"
       end
 
+      def add_foreign_key(referencing_table, referenced_table, options = {})
+      end
+
+      def remove_foreign_key(referencing_table, referenced_table_or_options)
+      end
+
       def rename_table(name, new_name)
         execute "ALTER TABLE #{quote_table_name(name)} RENAME TO #{quote_table_name(new_name)}"
       end
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index c8e1b4f..6bbe934 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -6,7 +6,7 @@ module ActiveRecord
   # output format (i.e., ActiveRecord::Schema).
   class SchemaDumper #:nodoc:
     private_class_method :new
-    
+
     ##
     # :singleton-method:
     # A list of tables which should not be dumped to the schema. 
@@ -38,7 +38,7 @@ module ActiveRecord
       def header(stream)
         define_params = @version ? ":version => #{@version}" : ""
 
-        stream.puts <<HEADER
+        stream.puts <<-HEADER
 # This file is auto-generated from the current state of the database. Instead of editing this file, 
 # please use the migrations feature of Active Record to incrementally modify your database, and
 # then regenerate this schema definition.
@@ -60,6 +60,8 @@ HEADER
       end
 
       def tables(stream)
+        fks = StringIO.new
+
         @connection.tables.sort.each do |tbl|
           next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|
             case ignored
@@ -70,7 +72,11 @@ HEADER
             end
           end 
           table(tbl, stream)
+          foreign_keys(tbl, fks)
         end
+
+        fks.rewind
+        stream.print fks.read
       end
 
       def table(table, stream)
@@ -185,5 +191,30 @@ HEADER
           stream.puts
         end
       end
+
+      def foreign_keys(table_name, stream)
+        if (foreign_keys = @connection.foreign_keys(table_name)).any?
+          add_foreign_key_statements = foreign_keys.map do |foreign_key|
+            statement_parts = [ ('add_foreign_key ' + foreign_key.referencing_table.inspect) ]
+            statement_parts << foreign_key.referenced_table.inspect
+            statement_parts << (':name => ' + foreign_key.options[:name].inspect)
+            
+            if foreign_key.options[:column] != "#{foreign_key.referenced_table.singularize}_id"
+              statement_parts << (':column => ' + foreign_key.options[:column].inspect)
+            end
+            if foreign_key.options[:primary_key] != 'id'
+              statement_parts << (':primary_key => ' + foreign_key.options[:primary_key].inspect)
+            end
+            if foreign_key.options[:dependent].present?
+              statement_parts << (':dependent => ' + foreign_key.options[:dependent].inspect)
+            end
+
+            '  ' + statement_parts.join(', ')
+          end
+
+          stream.puts add_foreign_key_statements.sort.join("\n")
+          stream.puts
+        end
+      end
   end
 end
-- 
1.7.0.4


From e9e40c108fb403fb498b0d6e5c468a00c20604a9 Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 09:54:46 -0700
Subject: [PATCH 2/4] Tests, tweaks and docs

---
 .../abstract/schema_statements.rb                  |    6 ++--
 .../connection_adapters/abstract_adapter.rb        |    6 +++++
 .../connection_adapters/sqlite_adapter.rb          |    4 +++
 activerecord/lib/active_record/migration.rb        |    3 ++
 activerecord/test/cases/adapter_test.rb            |   24 ++++++++++++++++++-
 activerecord/test/cases/migration_test.rb          |   18 +++++++++++++++
 activerecord/test/cases/schema_dumper_test.rb      |    4 +++
 activerecord/test/schema/schema.rb                 |   24 +++++--------------
 railties/guides/source/migrations.textile          |    4 ++-
 9 files changed, 70 insertions(+), 23 deletions(-)

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 745e386..b2ac01d 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -368,11 +368,11 @@ module ActiveRecord
       #   remove_foreign_key :accounts, :column => :branch_id
       # Remove the foreign key named party_foreign_key in the accounts table.
       #   remove_foreign_key :accounts, :name => :party_foreign_key
-      def remove_foreign_key(referencing_table, referenced_table_or_options)
+      def remove_foreign_key(referencing_table, options)
         if Hash === options
           foreign_key_name = foreign_key_name(referencing_table, options)
         else
-          foreign_key_name = foreign_key_name(referencing_table, :column => "#{referenced_table.to_s.singularize}_id")
+          foreign_key_name = foreign_key_name(referencing_table, :column => "#{options.to_s.singularize}_id")
         end
 
         execute "ALTER TABLE #{quote_table_name(referencing_table)} DROP FOREIGN KEY #{quote_column_name(foreign_key_name)}"
@@ -389,7 +389,7 @@ module ActiveRecord
       end
 
       def foreign_key_dependency(options)
-        case options[:dependency]
+        case options[:dependent]
           when :nullify then "ON DELETE SET NULL"
           when :delete  then "ON DELETE CASCADE"
           else ""
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 6ffffc8..9ea3801 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -62,6 +62,12 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support foreign key constraints?  This is +true+
+      # for all adapters except sqlite.
+      def supports_foreign_keys?
+        true
+      end
+
       # Does this adapter support using DISTINCT within COUNT?  This is +true+
       # for all adapters except sqlite.
       def supports_count_distinct?
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 09ead91..b002e86 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -84,6 +84,10 @@ module ActiveRecord
         true
       end
 
+      def supports_foreign_keys?
+        false
+      end
+
       def requires_reloading?
         true
       end
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index c163fb9..d96de14 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -96,6 +96,9 @@ module ActiveRecord
   # * <tt>add_index(table_name, column_names, options)</tt>: Adds a new index with the name of the column. Other options include
   #   <tt>:name</tt> and <tt>:unique</tt> (e.g. <tt>{ :name => "users_name_index", :unique => true }</tt>).
   # * <tt>remove_index(table_name, index_name)</tt>: Removes the index specified by +index_name+.
+  # * <tt>add_foreign_key(referencing_table, referenced_table, options)</tt>: Adds a new foreign key to the referencing_table,
+  #   with a constraint on the primary key of the referenced_table. Options include <tt>:column</tt>, <tt>:name</tt>, <tt>:primary_key</tt>
+  #   and <tt>:dependent</tt>. (e.g. <tt>{:name => 'my_foreign_key', :column => 'author_id', :dependent => :delete})
   #
   # == Irreversible transformations
   #
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 9f78ae0..f8ff892 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -41,6 +41,26 @@ class AdapterTest < ActiveRecord::TestCase
     @connection.remove_index(:accounts, :name => idx_name) rescue nil
   end
 
+  def test_foreign_keys
+    fk_name = 'favorited_author'
+
+    if @connection.supports_foreign_keys?
+      foreign_keys = @connection.foreign_keys("author_favorites")
+      assert foreign_keys.empty?
+
+      @connection.add_foreign_key :author_favorites, :authors, :name => fk_name, :column => 'favorite_author_id', :dependent => :delete
+      @connection.foreign_keys("author_favorites").first.tap do |foreign_key|
+        assert_equal 'author_favorites', foreign_key.referencing_table
+        assert_equal 'authors', foreign_key.referenced_table
+        assert_equal fk_name, foreign_key.options[:name]
+        assert_equal 'favorite_author_id', foreign_key.options[:column]
+        assert_equal :delete, foreign_key.options[:dependent]
+      end
+    end
+  ensure
+    @connection.remove_foreign_key :author_favorites, :name => fk_name
+  end
+
   def test_current_database
     if @connection.respond_to?(:current_database)
       assert_equal ENV['ARUNIT_DB_NAME'] || "activerecord_unittest", @connection.current_database
@@ -136,7 +156,7 @@ class AdapterTest < ActiveRecord::TestCase
   end
 
   def test_foreign_key_violations_are_translated_to_specific_exception
-    unless @connection.adapter_name == 'SQLite'
+    if @connection.supports_foreign_keys?
       assert_raises(ActiveRecord::InvalidForeignKey) do
         # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
         if @connection.prefetch_primary_key?
@@ -151,7 +171,7 @@ class AdapterTest < ActiveRecord::TestCase
 
   def test_add_limit_offset_should_sanitize_sql_injection_for_limit_without_comas
     sql_inject = "1 select * from schema"
-      assert_equal " LIMIT 1", @connection.add_limit_offset!("", :limit => sql_inject)
+    assert_equal " LIMIT 1", @connection.add_limit_offset!("", :limit => sql_inject)
     if current_adapter?(:MysqlAdapter)
       assert_equal " LIMIT 7, 1", @connection.add_limit_offset!("", :limit => sql_inject, :offset => 7)
     else
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index e213986..67a464e 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -111,6 +111,17 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_add_foreign_key
+      Subscription.delete_all
+      Order.delete_all
+      assert_nothing_raised { Subscription.connection.add_foreign_key :subscriptions, :books }
+      assert_nothing_raised { Subscription.connection.remove_foreign_key :subscriptions, :books }
+      assert_nothing_raised { Subscription.connection.add_foreign_key :subscriptions, :books, :name => 'fk_subscribed_books' }
+      assert_nothing_raised { Subscription.connection.remove_foreign_key :subscriptions, :name => 'fk_subscribed_books' }
+      assert_nothing_raised { Order.connection.add_foreign_key :orders, :people, :column => 'billing_customer_id'}
+      assert_nothing_raised { Order.connection.remove_foreign_key :orders, :column => 'billing_customer_id' }
+    end
+
     def testing_table_with_only_foo_attribute
       Person.connection.create_table :testings, :id => false do |t|
         t.column :foo, :string
@@ -1606,6 +1617,13 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_foreign_key_creates_foreign_key
+      with_change_table do |t|
+        @connection.expects(:add_foreign_key).with(:delete_me, :bar, {:dependent => :delete})
+        t.foreign_key :bar, :dependent => :delete
+      end
+    end
+
     def test_change_changes_column
       with_change_table do |t|
         @connection.expects(:change_column).with(:delete_me, :bar, :string, {})
diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index 1c43e3c..3af5698 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -162,6 +162,10 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_equal 'add_index "companies", ["firm_id", "type", "rating", "ruby_type"], :name => "company_index"', index_definition
   end
 
+  def test_foreign_keys
+    output = standard_dump
+  end
+
   def test_schema_dump_should_honor_nonstandard_primary_keys
     output = standard_dump
     match = output.match(%r{create_table "movies"(.*)do})
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index bec4291..18698cf 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -1,10 +1,4 @@
 ActiveRecord::Schema.define do
-  def except(adapter_names_to_exclude)
-    unless [adapter_names_to_exclude].flatten.include?(adapter_name)
-      yield
-    end
-  end
-
   #put adapter specific setup here
   case adapter_name
     # For Firebird, set the sequence values 10000 when create_table is called;
@@ -545,18 +539,14 @@ ActiveRecord::Schema.define do
   create_table :zines, :force => true do |t|
     t.string :title
   end
-
-  except 'SQLite' do
-    # fk_test_has_fk should be before fk_test_has_pk
-    create_table :fk_test_has_fk, :force => true do |t|
-      t.integer :fk_id, :null => false
-    end
-
-    create_table :fk_test_has_pk, :force => true do |t|
-    end
-
-    execute "ALTER TABLE fk_test_has_fk ADD CONSTRAINT fk_name FOREIGN KEY (#{quote_column_name 'fk_id'}) REFERENCES #{quote_table_name 'fk_test_has_pk'} (#{quote_column_name 'id'})"
+  
+  create_table :fk_test_has_fk, :force => true do |t|
+    t.integer :fk_id, :null => false
+  end
+  
+  create_table :fk_test_has_pk, :force => true do |t|
   end
+  add_foreign_key :fk_test_has_fk, :fk_test_has_pk, :column => :fk_id, :name => 'fk_id'
 end
 
 Course.connection.create_table :courses, :force => true do |t|
diff --git a/railties/guides/source/migrations.textile b/railties/guides/source/migrations.textile
index 558cbb4..c3fca91 100644
--- a/railties/guides/source/migrations.textile
+++ b/railties/guides/source/migrations.textile
@@ -75,6 +75,8 @@ Active Record provides methods that perform common data definition tasks in a da
 * +remove_column+
 * +add_index+
 * +remove_index+
+* +add_foreign_key+
+* +remove_foreign_key+
 
 If you need to perform tasks specific to your database (for example create a "foreign key":#active-record-and-referential-integrity constraint) then the +execute+ function allows you to execute arbitrary SQL. A migration is just a regular Ruby class so you're not limited to these functions. For example after adding a column you could write code to set the value of that column for existing records (if necessary using your models).
 
@@ -564,7 +566,7 @@ ActiveRecord::Schema.define(:version => 20080906171750) do
 end
 </ruby>
 
-In many ways this is exactly what it is. This file is created by inspecting the database and expressing its structure using +create_table+, +add_index+, and so on. Because this is database independent it could be loaded into any database that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases.
+In many ways this is exactly what it is. This file is created by inspecting the database and expressing its structure using +create_table+, +add_index+, and +add_foreign_key+. Because this is database independent it could be loaded into any database that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases.
 
 There is however a trade-off: +db/schema.rb+ cannot express database specific items such as foreign key constraints, triggers or stored procedures. While in a migration you can execute custom SQL statements, the schema dumper cannot reconstitute those statements from the database. If you are using features like this then you should set the schema format to +:sql+.
 
-- 
1.7.0.4


From 818304962e4164e5ca7e89f1ad8277a0f04cf890 Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 10:02:18 -0700
Subject: [PATCH 3/4] Add test for t.remove_foreign_key

---
 activerecord/test/cases/migration_test.rb |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index 67a464e..d64ecc8 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -1,7 +1,9 @@
 require "cases/helper"
 require 'bigdecimal/util'
 
+require 'models/order'
 require 'models/person'
+require 'models/subscription'
 require 'models/topic'
 require 'models/developer'
 
@@ -1666,6 +1668,13 @@ if ActiveRecord::Base.connection.supports_migrations?
       end
     end
 
+    def test_remove_foreign_key
+      with_change_table do |t|
+        @connection.expects(:remove_foreign_key).with(:delete_me, {:name => 'foo'})
+        t.remove_foreign_key :name => 'foo'
+      end
+    end
+
     def test_rename_renames_column
       with_change_table do |t|
         @connection.expects(:rename_column).with(:delete_me, :bar, :baz)
-- 
1.7.0.4


From 4304633099b638e043e4820f6bbbe645323dc746 Mon Sep 17 00:00:00 2001
From: Matthew <developer@matthewhiggins.com>
Date: Thu, 8 Apr 2010 10:29:30 -0700
Subject: [PATCH 4/4] Separate table dumps from foreign key dumps

---
 activerecord/lib/active_record/schema_dumper.rb |   18 ++++++------------
 1 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index 6bbe934..6e206c6 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -22,7 +22,8 @@ module ActiveRecord
 
     def dump(stream)
       header(stream)
-      tables(stream)
+      table_names.each { |tbl| table(tbl, stream) }
+      table_names.each { |tbl| foreign_keys(tbl, stream) }
       trailer(stream)
       stream
     end
@@ -59,24 +60,17 @@ HEADER
         stream.puts "end"
       end
 
-      def tables(stream)
-        fks = StringIO.new
-
-        @connection.tables.sort.each do |tbl|
-          next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|
+      def table_names
+        @connection.tables.sort.reject do |tbl|
+          ['schema_migrations', ignore_tables].flatten.any? do |ignored|
             case ignored
             when String; tbl == ignored
             when Regexp; tbl =~ ignored
             else
               raise StandardError, 'ActiveRecord::SchemaDumper.ignore_tables accepts an array of String and / or Regexp values.'
             end
-          end 
-          table(tbl, stream)
-          foreign_keys(tbl, fks)
+          end
         end
-
-        fks.rewind
-        stream.print fks.read
       end
 
       def table(table, stream)
-- 
1.7.0.4