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Reimplementation of validates_uniqueness_of that works optimally with MySQL.

View validates_uniqueness_of.rb
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module ActiveRecord::Validations::ClassMethods
def validates_uniqueness_of(*attr_names)
configuration = { :case_sensitive => true }
configuration.update(attr_names.extract_options!)
validates_each(attr_names,configuration) do |record, attr_name, value|
# The check for an existing value should be run from a class that
# isn't abstract. This means working down from the current class
# (self), to the first non-abstract class. Since classes don't know
# their subclasses, we have to build the hierarchy between self and
# the record's class.
class_hierarchy = [record.class]
while class_hierarchy.first != self
class_hierarchy.insert(0, class_hierarchy.first.superclass)
end
# Now we can work our way down the tree to the first non-abstract
# class (which has a database table to query from).
finder_class = class_hierarchy.detect { |klass| !klass.abstract_class? }
column = finder_class.columns_hash[attr_name.to_s]
if value.nil?
comparison_operator = "IS ?"
elsif column.text?
if configuration[:case_sensitive] then
comparison_operator = "#{connection.case_sensitive_equality_operator} BINARY ?"
else
comparison_operator = "#{connection.case_sensitive_equality_operator} ?"
end
value = column.limit ? value.to_s[0, column.limit] : value.to_s
else
comparison_operator = "= ?"
end
sql_attribute = "#{record.class.quoted_table_name}.#{connection.quote_column_name(attr_name)}"
condition_sql = "#{sql_attribute} #{comparison_operator}"
condition_params = [value]
if scope = configuration[:scope]
Array(scope).map do |scope_item|
scope_value = record.send(scope_item)
condition_sql << " AND " << attribute_condition("#{record.class.quoted_table_name}.#{scope_item}", scope_value)
condition_params << scope_value
end
end
unless record.new_record?
condition_sql << " AND #{record.class.quoted_table_name}.#{record.class.primary_key} <> ?"
condition_params << record.send(:id)
end
finder_class.with_exclusive_scope do
if finder_class.exists?([condition_sql, *condition_params])
record.errors.add(attr_name, :taken, :default => configuration[:message], :value => value)
end
end
end
end
end
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