Module ActiveModel::Validations::ClassMethods

Check if method is an attribute method or not.

Copy validators on inheritance.

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

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

class Comment
  include ActiveModel::Validations

  validate :must_be_friends

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

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

class Comment
  include ActiveModel::Validations

  validate do |comment|
    comment.must_be_friends
  end

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

Or with a block where self points to the current record to be validated:

class Comment
  include ActiveModel::Validations

  validate do
    errors.add(:base, "Must be friends to leave a comment") unless commenter.friend_of?(commentee)
  end
end

This method is a shortcut to all default validators and any custom validator classes ending in ‘Validator’. Note that Rails default validators can be overridden inside specific classes by creating custom validator classes in their place such as PresenceValidator.

Examples of using the default rails validators:

validates :terms, :acceptance => true
validates :password, :confirmation => true
validates :username, :exclusion => { :in => %w(admin superuser) }
validates :email, :format => { :with => %r\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/, :on => :create }
validates :age, :inclusion => { :in => 0..9 }
validates :first_name, :length => { :maximum => 30 }
validates :age, :numericality => true
validates :username, :presence => true
validates :username, :uniqueness => true

The power of the validates method comes when using custom validators and default validators in one call for a given attribute e.g.

class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors.add attribute, (options[:message] || "is not an email") unless
      value =~ %r\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/
  end
end

class Person
  include ActiveModel::Validations
  attr_accessor :name, :email

  validates :name, :presence => true, :uniqueness => true, :length => { :maximum => 100 }
  validates :email, :presence => true, :email => true
end

Validator classes may also exist within the class being validated allowing custom modules of validators to be included as needed e.g.

class Film
  include ActiveModel::Validations

  class TitleValidator < ActiveModel::EachValidator
    def validate_each(record, attribute, value)
      record.errors.add attribute, "must start with 'the'" unless value =~ %r\Athe/
    end
  end

  validates :name, :title => true
end

Additionally validator classes may be in another namespace and still used within any class.

validates :name, :'film/title' => true

The validators hash can also handle regular expressions, ranges, arrays and strings in shortcut form, e.g.

validates :email, :format => %r@/
validates :gender, :inclusion => %w(male female)
validates :password, :length => 6..20

When using shortcut form, ranges and arrays are passed to your validator’s initializer as +options+ while other types including regular expressions and strings are passed as +options+

Finally, the options :if, :unless, :on, :allow_blank, :allow_nil and :strict can be given to one specific validator, as a hash:

validates :password, :presence => { :if => :password_required? }, :confirmation => true

Or to all at the same time:

validates :password, :presence => true, :confirmation => true, :if => :password_required?

This method is used to define validation that cannot be corrected by end user and is considered exceptional. So each validator defined with bang or :strict option set to true will always raise ActiveModel::StrictValidationFailed instead of adding error when validation fails. See validates for more information about validation itself.

Validates each attribute against a block.

class Person
  include ActiveModel::Validations

  attr_accessor :first_name, :last_name

  validates_each :first_name, :last_name do |record, attr, value|
    record.errors.add attr, 'starts with z.' if value.to_s[0] == zz
  end
end

Options:

• :on - Specifies the context where this validation is active (e.g. :on => :create or :on => :custom_validation_context)

• :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.

If you pass any additional configuration options, they will be passed to the class and available as options:

class Person
  include ActiveModel::Validations
  validates_with MyValidator, :my_custom_key => "my custom value"
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    options[:my_custom_key] # => "my custom value"
  end
end

List all validators that are being used to validate the model using validates_with method.

List all validators that being used to validate a specific attribute.

When creating custom validators, it might be useful to be able to specify additional default keys. This can be done by overwriting this method.