module ActiveModel module Validations module ClassMethods # Validates whether the value of the specified attributes are unique across the system. Useful for making sure that only one user # can be named "davidhh". # # class Person < ActiveRecord::Base # validates_uniqueness_of :user_name, :scope => :account_id # end # # It can also validate whether the value of the specified attributes are unique based on multiple scope parameters. For example, # making sure that a teacher can only be on the schedule once per semester for a particular class. # # class TeacherSchedule < ActiveRecord::Base # validates_uniqueness_of :teacher_id, :scope => [:semester_id, :class_id] # end # # When the record is created, a check is performed to make sure that no record exists in the database with the given value for the specified # attribute (that maps to a column). When the record is updated, the same check is made but disregarding the record itself. # # Because this check is performed outside the database there is still a chance that duplicate values # will be inserted in two parallel transactions. To guarantee against this you should create a # unique index on the field. See +add_index+ for more information. # # Configuration options: # * :message - Specifies a custom error message (default is: "has already been taken") # * :scope - One or more columns by which to limit the scope of the uniqueness constraint. # * :case_sensitive - Looks for an exact match. Ignored by non-text columns (+false+ by default). # * :allow_nil - If set to +true+, skips this validation if the attribute is +nil+ (default is: +false+) # * :allow_blank - If set to +true+, skips this validation if the attribute is blank (default is: +false+) # * :if - Specifies a method, proc or string to call to determine if the validation should # occur (e.g. :if => :allow_validation, or :if => Proc.new { |user| user.signup_step > 2 }). The # method, proc or string should return or evaluate to a true or false value. # * :unless - Specifies a method, proc or string to call to determine if the validation should # not occur (e.g. :unless => :skip_validation, or :unless => Proc.new { |user| user.signup_step <= 2 }). The # method, proc or string should return or evaluate to a true or false value. def validates_uniqueness_of(*attr_names) configuration = { :message => ActiveRecord::Errors.default_error_messages[:taken] } 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? } if value.nil? || (configuration[:case_sensitive] || !finder_class.columns_hash[attr_name.to_s].text?) condition_sql = "#{record.class.quoted_table_name}.#{attr_name} #{attribute_condition(value)}" condition_params = [value] else # sqlite has case sensitive SELECT query, while MySQL/Postgresql don't. # Hence, this is needed only for sqlite. condition_sql = "LOWER(#{record.class.quoted_table_name}.#{attr_name}) #{attribute_condition(value)}" condition_params = [value.downcase] end if scope = configuration[:scope] Array(scope).map do |scope_item| scope_value = record.send(scope_item) condition_sql << " AND #{record.class.quoted_table_name}.#{scope_item} #{attribute_condition(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 results = finder_class.with_exclusive_scope do connection.select_all( construct_finder_sql( :select => "#{attr_name}", :from => "#{finder_class.quoted_table_name}", :conditions => [condition_sql, *condition_params] ) ) end unless results.length.zero? found = true # As MySQL/Postgres don't have case sensitive SELECT queries, we try to find duplicate # column in ruby when case sensitive option if configuration[:case_sensitive] && finder_class.columns_hash[attr_name.to_s].text? found = results.any? { |a| a[attr_name.to_s] == value } end record.errors.add(attr_name, configuration[:message]) if found end end end end end end