All of the following validations are defined in the class scope of the model that you‘re interested in validating. They offer a more declarative way of specifying when the model is valid and when it is not. It is recommended to use these over the low-level calls to validate and validate_on_create when possible.

Methods
Constants
DEFAULT_VALIDATION_OPTIONS = { :on => :save, :allow_nil => false, :allow_blank => false, :message => nil
ALL_RANGE_OPTIONS = [ :is, :within, :in, :minimum, :maximum ].freeze
ALL_NUMERICALITY_CHECKS = { :greater_than => '>', :greater_than_or_equal_to => '>=', :equal_to => '==', :less_than => '<', :less_than_or_equal_to => '<=', :odd => 'odd?', :even => 'even?' }.freeze
Public Instance methods
create!(attributes = nil) {|object| ...}

Creates an object just like Base.create but calls save! instead of save so an exception is raised if the record is invalid.

     # File lib/active_record/validations.rb, line 880
880:       def create!(attributes = nil, &block)
881:         if attributes.is_a?(Array)
882:           attributes.collect { |attr| create!(attr, &block) }
883:         else
884:           object = new(attributes)
885:           yield(object) if block_given?
886:           object.save!
887:           object
888:         end
889:       end
validates_acceptance_of(*attr_names)

Encapsulates the pattern of wanting to validate the acceptance of a terms of service check box (or similar agreement). Example:

  class Person < ActiveRecord::Base
    validates_acceptance_of :terms_of_service
    validates_acceptance_of :eula, :message => "must be abided"
  end

If the database column does not exist, the terms_of_service attribute is entirely virtual. This check is performed only if terms_of_service is not nil and by default on save.

Configuration options:

  • :message - A custom error message (default is: "must be accepted").
  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :allow_nil - Skip validation if attribute is nil (default is true).
  • :accept - Specifies value that is considered accepted. The default value is a string "1", which makes it easy to relate to an HTML checkbox. This should be set to true if you are validating a database column, since the attribute is typecast from "1" to true before validation.
  • :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.
     # File lib/active_record/validations.rb, line 425
425:       def validates_acceptance_of(*attr_names)
426:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:accepted], :on => :save, :allow_nil => true, :accept => "1" }
427:         configuration.update(attr_names.extract_options!)
428: 
429:         db_cols = begin
430:           column_names
431:         rescue ActiveRecord::StatementInvalid
432:           []
433:         end
434:         names = attr_names.reject { |name| db_cols.include?(name.to_s) }
435:         attr_accessor(*names)
436: 
437:         validates_each(attr_names,configuration) do |record, attr_name, value|
438:           record.errors.add(attr_name, configuration[:message]) unless value == configuration[:accept]
439:         end
440:       end
validates_associated(*attr_names)

Validates whether the associated object or objects are all valid themselves. Works with any kind of association.

  class Book < ActiveRecord::Base
    has_many :pages
    belongs_to :library

    validates_associated :pages, :library
  end

Warning: If, after the above definition, you then wrote:

  class Page < ActiveRecord::Base
    belongs_to :book

    validates_associated :book
  end

this would specify a circular dependency and cause infinite recursion.

NOTE: This validation will not fail if the association hasn‘t been assigned. If you want to ensure that the association is both present and guaranteed to be valid, you also need to use validates_presence_of.

Configuration options:

  • :message - A custom error message (default is: "is invalid")
  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :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.
     # File lib/active_record/validations.rb, line 798
798:       def validates_associated(*attr_names)
799:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:invalid], :on => :save }
800:         configuration.update(attr_names.extract_options!)
801: 
802:         validates_each(attr_names, configuration) do |record, attr_name, value|
803:           record.errors.add(attr_name, configuration[:message]) unless
804:             (value.is_a?(Array) ? value : [value]).inject(true) { |v, r| (r.nil? || r.valid?) && v }
805:         end
806:       end
validates_confirmation_of(*attr_names)

Encapsulates the pattern of wanting to validate a password or email address field with a confirmation. Example:

  Model:
    class Person < ActiveRecord::Base
      validates_confirmation_of :user_name, :password
      validates_confirmation_of :email_address, :message => "should match confirmation"
    end

  View:
    <%= password_field "person", "password" %>
    <%= password_field "person", "password_confirmation" %>

The added password_confirmation attribute is virtual; it exists only as an in-memory attribute for validating the password. To achieve this, the validation adds accessors to the model for the confirmation attribute. NOTE: This check is performed only if password_confirmation is not nil, and by default only on save. To require confirmation, make sure to add a presence check for the confirmation attribute:

  validates_presence_of :password_confirmation, :if => :password_changed?

Configuration options:

  • :message - A custom error message (default is: "doesn‘t match confirmation").
  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :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.
     # File lib/active_record/validations.rb, line 391
391:       def validates_confirmation_of(*attr_names)
392:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:confirmation], :on => :save }
393:         configuration.update(attr_names.extract_options!)
394: 
395:         attr_accessor(*(attr_names.map { |n| "#{n}_confirmation" }))
396: 
397:         validates_each(attr_names, configuration) do |record, attr_name, value|
398:           record.errors.add(attr_name, configuration[:message]) unless record.send("#{attr_name}_confirmation").nil? or value == record.send("#{attr_name}_confirmation")
399:         end
400:       end
validates_each(*attrs) {|record, attr, value| ...}

Validates each attribute against a block.

  class Person < ActiveRecord::Base
    validates_each :first_name, :last_name do |record, attr, value|
      record.errors.add attr, 'starts with z.' if value[0] == ?z
    end
  end

Options:

  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :allow_nil - Skip validation if attribute is nil.
  • :allow_blank - Skip validation if attribute is blank.
  • :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.
     # File lib/active_record/validations.rb, line 349
349:       def validates_each(*attrs)
350:         options = attrs.extract_options!.symbolize_keys
351:         attrs   = attrs.flatten
352: 
353:         # Declare the validation.
354:         send(validation_method(options[:on] || :save), options) do |record|
355:           attrs.each do |attr|
356:             value = record.send(attr)
357:             next if (value.nil? && options[:allow_nil]) || (value.blank? && options[:allow_blank])
358:             yield record, attr, value
359:           end
360:         end
361:       end
validates_exclusion_of(*attr_names)

Validates that the value of the specified attribute is not in a particular enumerable object.

  class Person < ActiveRecord::Base
    validates_exclusion_of :username, :in => %w( admin superuser ), :message => "You don't belong here"
    validates_exclusion_of :age, :in => 30..60, :message => "This site is only for under 30 and over 60"
    validates_exclusion_of :format, :in => %w( mov avi ), :message => "extension %s is not allowed"
  end

Configuration options:

  • :in - An enumerable object of items that the value shouldn‘t be part of.
  • :message - Specifies a custom error message (default is: "is reserved").
  • :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.
     # File lib/active_record/validations.rb, line 754
754:       def validates_exclusion_of(*attr_names)
755:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:exclusion], :on => :save }
756:         configuration.update(attr_names.extract_options!)
757: 
758:         enum = configuration[:in] || configuration[:within]
759: 
760:         raise(ArgumentError, "An object with the method include? is required must be supplied as the :in option of the configuration hash") unless enum.respond_to?("include?")
761: 
762:         validates_each(attr_names, configuration) do |record, attr_name, value|
763:           record.errors.add(attr_name, configuration[:message] % value) if enum.include?(value)
764:         end
765:       end
validates_format_of(*attr_names)

Validates whether the value of the specified attribute is of the correct form by matching it against the regular expression provided.

  class Person < ActiveRecord::Base
    validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i, :on => :create
  end

Note: use \A and \Z to match the start and end of the string, ^ and $ match the start/end of a line.

A regular expression must be provided or else an exception will be raised.

Configuration options:

  • :message - A custom error message (default is: "is invalid").
  • :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).
  • :with - The regular expression used to validate the format with (note: must be supplied!).
  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :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.
     # File lib/active_record/validations.rb, line 692
692:       def validates_format_of(*attr_names)
693:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:invalid], :on => :save, :with => nil }
694:         configuration.update(attr_names.extract_options!)
695: 
696:         raise(ArgumentError, "A regular expression must be supplied as the :with option of the configuration hash") unless configuration[:with].is_a?(Regexp)
697: 
698:         validates_each(attr_names, configuration) do |record, attr_name, value|
699:           record.errors.add(attr_name, configuration[:message] % value) unless value.to_s =~ configuration[:with]
700:         end
701:       end
validates_inclusion_of(*attr_names)

Validates whether the value of the specified attribute is available in a particular enumerable object.

  class Person < ActiveRecord::Base
    validates_inclusion_of :gender, :in => %w( m f ), :message => "woah! what are you then!??!!"
    validates_inclusion_of :age, :in => 0..99
    validates_inclusion_of :format, :in => %w( jpg gif png ), :message => "extension %s is not included in the list"
  end

Configuration options:

  • :in - An enumerable object of available items.
  • :message - Specifies a custom error message (default is: "is not included in the list").
  • :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.
     # File lib/active_record/validations.rb, line 722
722:       def validates_inclusion_of(*attr_names)
723:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:inclusion], :on => :save }
724:         configuration.update(attr_names.extract_options!)
725: 
726:         enum = configuration[:in] || configuration[:within]
727: 
728:         raise(ArgumentError, "An object with the method include? is required must be supplied as the :in option of the configuration hash") unless enum.respond_to?("include?")
729: 
730:         validates_each(attr_names, configuration) do |record, attr_name, value|
731:           record.errors.add(attr_name, configuration[:message] % value) unless enum.include?(value)
732:         end
733:       end
validates_length_of(*attrs)

Validates that the specified attribute matches the length restrictions supplied. Only one option can be used at a time:

  class Person < ActiveRecord::Base
    validates_length_of :first_name, :maximum=>30
    validates_length_of :last_name, :maximum=>30, :message=>"less than %d if you don't mind"
    validates_length_of :fax, :in => 7..32, :allow_nil => true
    validates_length_of :phone, :in => 7..32, :allow_blank => true
    validates_length_of :user_name, :within => 6..20, :too_long => "pick a shorter name", :too_short => "pick a longer name"
    validates_length_of :fav_bra_size, :minimum => 1, :too_short => "please enter at least %d character"
    validates_length_of :smurf_leader, :is => 4, :message => "papa is spelled with %d characters... don't play me."
    validates_length_of :essay, :minimum => 100, :too_short => "Your essay must be at least %d words."), :tokenizer => lambda {|str| str.scan(/\w+/) }
  end

Configuration options:

  • :minimum - The minimum size of the attribute.
  • :maximum - The maximum size of the attribute.
  • :is - The exact size of the attribute.
  • :within - A range specifying the minimum and maximum size of the attribute.
  • :in - A synonym(or alias) for :within.
  • :allow_nil - Attribute may be nil; skip validation.
  • :allow_blank - Attribute may be blank; skip validation.
  • :too_long - The error message if the attribute goes over the maximum (default is: "is too long (maximum is %d characters)").
  • :too_short - The error message if the attribute goes under the minimum (default is: "is too short (min is %d characters)").
  • :wrong_length - The error message if using the :is method and the attribute is the wrong size (default is: "is the wrong length (should be %d characters)").
  • :message - The error message to use for a :minimum, :maximum, or :is violation. An alias of the appropriate too_long/too_short/wrong_length message.
  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :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.
  • :tokenizer - Specifies how to split up the attribute string. (e.g. :tokenizer => lambda {|str| str.scan(/\w+/)} to count words as in above example.) Defaults to lambda{ |value| value.split(//) } which counts individual characters.
This method is also aliased as validates_size_of
     # File lib/active_record/validations.rb, line 510
510:       def validates_length_of(*attrs)
511:         # Merge given options with defaults.
512:         options = {
513:           :too_long     => ActiveRecord::Errors.default_error_messages[:too_long],
514:           :too_short    => ActiveRecord::Errors.default_error_messages[:too_short],
515:           :wrong_length => ActiveRecord::Errors.default_error_messages[:wrong_length],
516:           :tokenizer    => lambda {|value| value.split(//)}
517:         }.merge(DEFAULT_VALIDATION_OPTIONS)
518:         options.update(attrs.extract_options!.symbolize_keys)
519: 
520:         # Ensure that one and only one range option is specified.
521:         range_options = ALL_RANGE_OPTIONS & options.keys
522:         case range_options.size
523:           when 0
524:             raise ArgumentError, 'Range unspecified.  Specify the :within, :maximum, :minimum, or :is option.'
525:           when 1
526:             # Valid number of options; do nothing.
527:           else
528:             raise ArgumentError, 'Too many range options specified.  Choose only one.'
529:         end
530: 
531:         # Get range option and value.
532:         option = range_options.first
533:         option_value = options[range_options.first]
534: 
535:         case option
536:           when :within, :in
537:             raise ArgumentError, ":#{option} must be a Range" unless option_value.is_a?(Range)
538: 
539:             too_short = options[:too_short] % option_value.begin
540:             too_long  = options[:too_long]  % option_value.end
541: 
542:             validates_each(attrs, options) do |record, attr, value|
543:               value = options[:tokenizer].call(value) if value.kind_of?(String)
544:               if value.nil? or value.size < option_value.begin
545:                 record.errors.add(attr, too_short)
546:               elsif value.size > option_value.end
547:                 record.errors.add(attr, too_long)
548:               end
549:             end
550:           when :is, :minimum, :maximum
551:             raise ArgumentError, ":#{option} must be a nonnegative Integer" unless option_value.is_a?(Integer) and option_value >= 0
552: 
553:             # Declare different validations per option.
554:             validity_checks = { :is => "==", :minimum => ">=", :maximum => "<=" }
555:             message_options = { :is => :wrong_length, :minimum => :too_short, :maximum => :too_long }
556: 
557:             message = (options[:message] || options[message_options[option]]) % option_value
558: 
559:             validates_each(attrs, options) do |record, attr, value|
560:               value = options[:tokenizer].call(value) if value.kind_of?(String)
561:               record.errors.add(attr, message) unless !value.nil? and value.size.method(validity_checks[option])[option_value]
562:             end
563:         end
564:       end
validates_numericality_of(*attr_names)

Validates whether the value of the specified attribute is numeric by trying to convert it to a float with Kernel.Float (if only_integer is false) or applying it to the regular expression /\A[+\-]?\d+\Z/ (if only_integer is set to true).

  class Person < ActiveRecord::Base
    validates_numericality_of :value, :on => :create
  end

Configuration options:

  • :message - A custom error message (default is: "is not a number").
  • :on - Specifies when this validation is active (default is :save, other options :create, :update).
  • :only_integer - Specifies whether the value has to be an integer, e.g. an integral value (default is false).
  • :allow_nil - Skip validation if attribute is nil (default is false). Notice that for fixnum and float columns empty strings are converted to nil.
  • :greater_than - Specifies the value must be greater than the supplied value.
  • :greater_than_or_equal_to - Specifies the value must be greater than or equal the supplied value.
  • :equal_to - Specifies the value must be equal to the supplied value.
  • :less_than - Specifies the value must be less than the supplied value.
  • :less_than_or_equal_to - Specifies the value must be less than or equal the supplied value.
  • :odd - Specifies the value must be an odd number.
  • :even - Specifies the value must be an even number.
  • :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.
     # File lib/active_record/validations.rb, line 834
834:       def validates_numericality_of(*attr_names)
835:         configuration = { :on => :save, :only_integer => false, :allow_nil => false }
836:         configuration.update(attr_names.extract_options!)
837: 
838: 
839:         numericality_options = ALL_NUMERICALITY_CHECKS.keys & configuration.keys
840: 
841:         (numericality_options - [ :odd, :even ]).each do |option|
842:           raise ArgumentError, ":#{option} must be a number" unless configuration[option].is_a?(Numeric)
843:         end
844: 
845:         validates_each(attr_names,configuration) do |record, attr_name, value|
846:           raw_value = record.send("#{attr_name}_before_type_cast") || value
847: 
848:           next if configuration[:allow_nil] and raw_value.nil?
849: 
850:           if configuration[:only_integer]
851:             unless raw_value.to_s =~ /\A[+-]?\d+\Z/
852:               record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
853:               next
854:             end
855:             raw_value = raw_value.to_i
856:           else
857:            begin
858:               raw_value = Kernel.Float(raw_value)
859:             rescue ArgumentError, TypeError
860:               record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
861:               next
862:             end
863:           end
864: 
865:           numericality_options.each do |option|
866:             case option
867:               when :odd, :even
868:                 record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[option]) unless raw_value.to_i.method(ALL_NUMERICALITY_CHECKS[option])[]
869:               else
870:                 message = configuration[:message] || ActiveRecord::Errors.default_error_messages[option]
871:                 message = message % configuration[option] if configuration[option]
872:                 record.errors.add(attr_name, message) unless raw_value.method(ALL_NUMERICALITY_CHECKS[option])[configuration[option]]
873:             end
874:           end
875:         end
876:       end
validates_presence_of(*attr_names)

Validates that the specified attributes are not blank (as defined by Object#blank?). Happens by default on save. Example:

  class Person < ActiveRecord::Base
    validates_presence_of :first_name
  end

The first_name attribute must be in the object and it cannot be blank.

If you want to validate the presence of a boolean field (where the real values are true and false), you will want to use validates_inclusion_of :field_name, :in => [true, false] This is due to the way Object#blank? handles boolean values. false.blank? # => true

Configuration options:

  • message - A custom error message (default is: "can‘t be blank").
  • on - Specifies when this validation is active (default is :save, other options :create, :update).
  • 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.
     # File lib/active_record/validations.rb, line 464
464:       def validates_presence_of(*attr_names)
465:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:blank], :on => :save }
466:         configuration.update(attr_names.extract_options!)
467: 
468:         # can't use validates_each here, because it cannot cope with nonexistent attributes,
469:         # while errors.add_on_empty can
470:         send(validation_method(configuration[:on]), configuration) do |record|
471:           record.errors.add_on_blank(attr_names, configuration[:message])
472:         end
473:       end
validates_size_of(*attrs)
validates_uniqueness_of(*attr_names)

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.
     # File lib/active_record/validations.rb, line 602
602:       def validates_uniqueness_of(*attr_names)
603:         configuration = { :message => ActiveRecord::Errors.default_error_messages[:taken], :case_sensitive => true }
604:         configuration.update(attr_names.extract_options!)
605: 
606:         validates_each(attr_names,configuration) do |record, attr_name, value|
607:           # The check for an existing value should be run from a class that
608:           # isn't abstract. This means working down from the current class
609:           # (self), to the first non-abstract class. Since classes don't know
610:           # their subclasses, we have to build the hierarchy between self and
611:           # the record's class.
612:           class_hierarchy = [record.class]
613:           while class_hierarchy.first != self
614:             class_hierarchy.insert(0, class_hierarchy.first.superclass)
615:           end
616: 
617:           # Now we can work our way down the tree to the first non-abstract
618:           # class (which has a database table to query from).
619:           finder_class = class_hierarchy.detect { |klass| !klass.abstract_class? }
620: 
621:           if value.nil? || (configuration[:case_sensitive] || !finder_class.columns_hash[attr_name.to_s].text?)
622:             condition_sql = "#{record.class.quoted_table_name}.#{attr_name} #{attribute_condition(value)}"
623:             condition_params = [value]
624:           else
625:             # sqlite has case sensitive SELECT query, while MySQL/Postgresql don't.
626:             # Hence, this is needed only for sqlite.
627:             condition_sql = "LOWER(#{record.class.quoted_table_name}.#{attr_name}) #{attribute_condition(value)}"
628:             condition_params = [value.downcase]
629:           end
630: 
631:           if scope = configuration[:scope]
632:             Array(scope).map do |scope_item|
633:               scope_value = record.send(scope_item)
634:               condition_sql << " AND #{record.class.quoted_table_name}.#{scope_item} #{attribute_condition(scope_value)}"
635:               condition_params << scope_value
636:             end
637:           end
638: 
639:           unless record.new_record?
640:             condition_sql << " AND #{record.class.quoted_table_name}.#{record.class.primary_key} <> ?"
641:             condition_params << record.send(:id)
642:           end
643: 
644:           results = finder_class.with_exclusive_scope do
645:             connection.select_all(
646:               construct_finder_sql(
647:                 :select     => "#{connection.quote_column_name(attr_name)}",
648:                 :from       => "#{finder_class.quoted_table_name}",
649:                 :conditions => [condition_sql, *condition_params]
650:               )
651:             )
652:           end
653: 
654:           unless results.length.zero?
655:             found = true
656: 
657:             # As MySQL/Postgres don't have case sensitive SELECT queries, we try to find duplicate
658:             # column in ruby when case sensitive option
659:             if configuration[:case_sensitive] && finder_class.columns_hash[attr_name.to_s].text?
660:               found = results.any? { |a| a[attr_name.to_s] == value }
661:             end
662: 
663:             record.errors.add(attr_name, configuration[:message]) if found
664:           end
665:         end
666:       end