Module: ActiveRecord::Validations::ClassMethods

Defined in:
lib/active_record/validations.rb

Overview

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.

Constant Summary collapse

DEFAULT_VALIDATION_OPTIONS = 
{
  :on => :save,
  :allow_nil => false,
  :allow_blank => false,
  :message => nil
}.freeze
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

Instance Method Summary collapse

Instance Method Details

#condition_block?(condition) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/active_record/validations.rb', line 342

def condition_block?(condition)
  condition.respond_to?("call") && (condition.arity == 1 || condition.arity == -1)
end

#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.



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# File 'lib/active_record/validations.rb', line 904

def create!(attributes = nil)
  if attributes.is_a?(Array)
    attributes.collect { |attr| create!(attr) }
  else
    object = new(attributes)
    object.save!
    object
  end
end

#evaluate_condition(condition, record) ⇒ Object

Determine from the given condition (whether a block, procedure, method or string) whether or not to validate the record. See #validates_each.



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# File 'lib/active_record/validations.rb', line 348

def evaluate_condition(condition, record)
  case condition
    when Symbol; record.send(condition)
    when String; eval(condition, record.send(:binding))
    else
      if condition_block?(condition)
        condition.call(record)
      else
        raise(
          ActiveRecordError,
          "Validations need to be either a symbol, string (to be eval'ed), proc/method, or " +
          "class implementing a static validation method"
        )
      end
    end
end

#validate(*methods, &block) ⇒ Object

Adds a validation method or block to the class. This is useful when overriding the #validate instance method becomes too unwieldly and you’re looking for more descriptive declaration of your validations.

This can be done with a symbol pointing to a method:

class Comment < ActiveRecord::Base
  validate :must_be_friends

  def must_be_friends
    errors.add_to_base("Must be friends to leave a comment") unless commenter.friend_of?(commentee)
  end
end

Or with a block which is passed the current record to be validated:

class Comment < ActiveRecord::Base
  validate do |comment|
    comment.must_be_friends
  end

  def must_be_friends
    errors.add_to_base("Must be friends to leave a comment") unless commenter.friend_of?(commentee)
  end
end

This usage applies to #validate_on_create and #validate_on_update as well.



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# File 'lib/active_record/validations.rb', line 327

def validate(*methods, &block)
  methods << block if block_given?
  write_inheritable_set(:validate, methods)
end

#validate_on_create(*methods, &block) ⇒ Object 



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# File 'lib/active_record/validations.rb', line 332

def validate_on_create(*methods, &block)
  methods << block if block_given?
  write_inheritable_set(:validate_on_create, methods)
end

#validate_on_update(*methods, &block) ⇒ Object 



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# File 'lib/active_record/validations.rb', line 337

def validate_on_update(*methods, &block)
  methods << block if block_given?
  write_inheritable_set(:validate_on_update, methods)
end

#validates_acceptance_of(*attr_names) ⇒ Object

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.



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# File 'lib/active_record/validations.rb', line 462

def validates_acceptance_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:accepted], :on => :save, :allow_nil => true, :accept => "1" }
  configuration.update(attr_names.extract_options!)

  db_cols = begin
    column_names
  rescue ActiveRecord::StatementInvalid
    []
  end
  names = attr_names.reject { |name| db_cols.include?(name.to_s) }
  attr_accessor(*names)

  validates_each(attr_names,configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message]) unless value == configuration[:accept]
  end
end

#validates_associated(*attr_names) ⇒ Object

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.



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# File 'lib/active_record/validations.rb', line 824

def validates_associated(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:invalid], :on => :save }
  configuration.update(attr_names.extract_options!)

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message]) unless
      (value.is_a?(Array) ? value : [value]).inject(true) { |v, r| (r.nil? || r.valid?) && v }
  end
end

#validates_confirmation_of(*attr_names) ⇒ Object

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 acccessors 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.



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# File 'lib/active_record/validations.rb', line 428

def validates_confirmation_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:confirmation], :on => :save }
  configuration.update(attr_names.extract_options!)

  attr_accessor(*(attr_names.map { |n| "#{n}_confirmation" }))

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message]) unless record.send("#{attr_name}_confirmation").nil? or value == record.send("#{attr_name}_confirmation")
  end
end

#validates_each(*attrs) ⇒ Object

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.



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# File 'lib/active_record/validations.rb', line 383

def validates_each(*attrs)
  options = attrs.extract_options!.symbolize_keys
  attrs   = attrs.flatten

  # Declare the validation.
  send(validation_method(options[:on] || :save)) do |record|
    # Don't validate when there is an :if condition and that condition is false or there is an :unless condition and that condition is true
    unless (options[:if] && !evaluate_condition(options[:if], record)) || (options[:unless] && evaluate_condition(options[:unless], record))
      attrs.each do |attr|
        value = record.send(attr)
        next if (value.nil? && options[:allow_nil]) || (value.blank? && options[:allow_blank])
        yield record, attr, value
      end
    end
  end
end

#validates_exclusion_of(*attr_names) ⇒ Object

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 customer error message (default is: “is reserved”)

  • allow_nil - If set to true, skips this validation if the attribute is null (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.

Raises:

  • (ArgumentError) 


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# File 'lib/active_record/validations.rb', line 780

def validates_exclusion_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:exclusion], :on => :save }
  configuration.update(attr_names.extract_options!)

  enum = configuration[:in] || configuration[:within]

  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?")

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message] % value) if enum.include?(value)
  end
end

#validates_format_of(*attr_names) ⇒ Object

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”)

  • 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.

Raises:

  • (ArgumentError) 


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# File 'lib/active_record/validations.rb', line 718

def validates_format_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:invalid], :on => :save, :with => nil }
  configuration.update(attr_names.extract_options!)

  raise(ArgumentError, "A regular expression must be supplied as the :with option of the configuration hash") unless configuration[:with].is_a?(Regexp)

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message]) unless value.to_s =~ configuration[:with]
  end
end

#validates_inclusion_of(*attr_names) ⇒ Object

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 customer error message (default is: “is not included in the list”)

  • allow_nil - If set to true, skips this validation if the attribute is null (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.

Raises:

  • (ArgumentError) 


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# File 'lib/active_record/validations.rb', line 748

def validates_inclusion_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:inclusion], :on => :save }
  configuration.update(attr_names.extract_options!)

  enum = configuration[:in] || configuration[:within]

  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?")

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message] % value) unless enum.include?(value)
  end
end

#validates_length_of(*attrs) ⇒ Object Also known as: validates_size_of

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."
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.



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# File 'lib/active_record/validations.rb', line 557

def validates_length_of(*attrs)
  # Merge given options with defaults.
  options = {
    :too_long     => ActiveRecord::Errors.default_error_messages[:too_long],
    :too_short    => ActiveRecord::Errors.default_error_messages[:too_short],
    :wrong_length => ActiveRecord::Errors.default_error_messages[:wrong_length]
  }.merge(DEFAULT_VALIDATION_OPTIONS)
  options.update(attrs.extract_options!.symbolize_keys)

  # Ensure that one and only one range option is specified.
  range_options = ALL_RANGE_OPTIONS & options.keys
  case range_options.size
    when 0
      raise ArgumentError, 'Range unspecified.  Specify the :within, :maximum, :minimum, or :is option.'
    when 1
      # Valid number of options; do nothing.
    else
      raise ArgumentError, 'Too many range options specified.  Choose only one.'
  end

  # Get range option and value.
  option = range_options.first
  option_value = options[range_options.first]

  case option
    when :within, :in
      raise ArgumentError, ":#{option} must be a Range" unless option_value.is_a?(Range)

      too_short = options[:too_short] % option_value.begin
      too_long  = options[:too_long]  % option_value.end

      validates_each(attrs, options) do |record, attr, value|
        if value.nil? or value.split(//).size < option_value.begin
          record.errors.add(attr, too_short)
        elsif value.split(//).size > option_value.end
          record.errors.add(attr, too_long)
        end
      end
    when :is, :minimum, :maximum
      raise ArgumentError, ":#{option} must be a nonnegative Integer" unless option_value.is_a?(Integer) and option_value >= 0

      # Declare different validations per option.
      validity_checks = { :is => "==", :minimum => ">=", :maximum => "<=" }
      message_options = { :is => :wrong_length, :minimum => :too_short, :maximum => :too_long }

      message = (options[:message] || options[message_options[option]]) % option_value

      validates_each(attrs, options) do |record, attr, value|
        if value.kind_of?(String)
          record.errors.add(attr, message) unless !value.nil? and value.split(//).size.method(validity_checks[option])[option_value]
        else
          record.errors.add(attr, message) unless !value.nil? and value.size.method(validity_checks[option])[option_value]
        end
      end
  end
end

#validates_numericality_of(*attr_names) ⇒ Object

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



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# File 'lib/active_record/validations.rb', line 860

def validates_numericality_of(*attr_names)
  configuration = { :on => :save, :only_integer => false, :allow_nil => false }
  configuration.update(attr_names.extract_options!)


  numericality_options = ALL_NUMERICALITY_CHECKS.keys & configuration.keys

  (numericality_options - [ :odd, :even ]).each do |option|
    raise ArgumentError, ":#{option} must be a number" unless configuration[option].is_a?(Numeric)
  end

  validates_each(attr_names,configuration) do |record, attr_name, value|
    raw_value = record.send("#{attr_name}_before_type_cast") || value

    next if configuration[:allow_nil] and raw_value.nil?

    if configuration[:only_integer]
      unless raw_value.to_s =~ /\A[+-]?\d+\Z/
        record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
        next
      end
      raw_value = raw_value.to_i
    else
     begin
        raw_value = Kernel.Float(raw_value.to_s)
      rescue ArgumentError, TypeError
        record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[:not_a_number])
        next
      end
    end

    numericality_options.each do |option|
      case option
        when :odd, :even
          record.errors.add(attr_name, configuration[:message] || ActiveRecord::Errors.default_error_messages[option]) unless raw_value.to_i.method(ALL_NUMERICALITY_CHECKS[option])[]
        else
          record.errors.add(attr_name, configuration[:message] || (ActiveRecord::Errors.default_error_messages[option] % configuration[option])) unless raw_value.method(ALL_NUMERICALITY_CHECKS[option])[configuration[option]]
      end
    end
  end
end

#validates_presence_of(*attr_names) ⇒ Object

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.

Warning

Validate the presence of the foreign key, not the instance variable itself. Do this:

validates_presence_of :invoice_id

Not this:

validates_presence_of :invoice

If you validate the presence of the associated object, you will get failures on saves when both the parent object and the child object are new.



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# File 'lib/active_record/validations.rb', line 512

def validates_presence_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:blank], :on => :save }
  configuration.update(attr_names.extract_options!)

  # can't use validates_each here, because it cannot cope with nonexistent attributes,
  # while errors.add_on_empty can
	send(validation_method(configuration[:on])) do |record|
	  unless (configuration[:if] && !evaluate_condition(configuration[:if], record)) || (configuration[:unless] && evaluate_condition(configuration[:unless], record))
	    record.errors.add_on_blank(attr_names, configuration[:message])
	  end
	end
end

#validates_uniqueness_of(*attr_names) ⇒ Object

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 create_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 uniquness constraint.

  • case_sensitive - Looks for an exact match. Ignored by non-text columns (true by default).

  • allow_nil - If set to true, skips this validation if the attribute is null (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.



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# File 'lib/active_record/validations.rb', line 650

def validates_uniqueness_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:taken], :case_sensitive => true }
  configuration.update(attr_names.extract_options!)

  validates_each(attr_names,configuration) do |record, attr_name, value|
    if value.nil? || (configuration[:case_sensitive] || !columns_hash[attr_name.to_s].text?)
      condition_sql = "#{record.class.table_name}.#{attr_name} #{attribute_condition(value)}"
      condition_params = [value]
    else
      condition_sql = "LOWER(#{record.class.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.table_name}.#{scope_item} #{attribute_condition(scope_value)}"
        condition_params << scope_value
      end
    end

    unless record.new_record?
      condition_sql << " AND #{record.class.table_name}.#{record.class.primary_key} <> ?"
      condition_params << record.send(:id)
    end

    # 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 finder_class.find(:first, :conditions => [condition_sql, *condition_params])
      record.errors.add(attr_name, configuration[:message])
    end
  end
end