module ActiveModel::Validations::ClassMethods

Returns true if attribute is an attribute method, false otherwise.

class Person
  include ActiveModel::Validations

  attr_accessor :name
end

User.attribute_method?(:name) # => true
User.attribute_method?(:age)  # => false

Clears all of the validators and validations.

Note that this will clear anything that is being used to validate the model for both the validates_with and validate methods. It clears the validators that are created with an invocation of validates_with and the callbacks that are set by an invocation of validate.

class Person
  include ActiveModel::Validations

  validates_with MyValidator
  validates_with OtherValidator, on: :create
  validates_with StrictValidator, strict: true
  validate :cannot_be_robot

  def cannot_be_robot
    errors.add(:base, 'A person cannot be a robot') if person_is_robot
  end
end

Person.validators
# => [
#      #<MyValidator:0x007fbff403e808 @options={}>,
#      #<OtherValidator:0x007fbff403d930 @options={on: :create}>,
#      #<StrictValidator:0x007fbff3204a30 @options={strict:true}>
#    ]

If one runs Person.clear_validators! and then checks to see what validators this class has, you would obtain:

Person.validators # => []

Also, the callback set by validate :cannot_be_robot will be erased so that:

Person._validate_callbacks.empty?  # => true

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

Note that the return value of validation methods is not relevant. It’s not possible to halt the validate callback chain.

Options:

• :on - Specifies the contexts where this validation is active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. on: :create or on: :custom_validation_context or on: [:create, :custom_validation_context])

• :except_on - Specifies the contexts where this validation is not active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. except: :create or except_on: :custom_validation_context or except_on: [:create, :custom_validation_context])

• :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.

NOTE: Calling validate multiple times on the same method will overwrite previous definitions.

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

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

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

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

  validates :name, presence: 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.

class Film
  include ActiveModel::Validations

  class TitleValidator < ActiveModel::EachValidator
    def validate_each(record, attribute, value)
      record.errors.add attribute, "must start with 'the'" unless /\Athe/i.match?(value)
    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.

validates :email, format: /@/
validates :role, inclusion: %w(admin contributor)
validates :password, length: 6..20

When using shortcut form, ranges and arrays are passed to your validator’s initializer as options[:in] while other types including regular expressions and strings are passed as options[:with].

There is also a list of options that could be used along with validators:

• :on - Specifies the contexts where this validation is active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. on: :create or on: :custom_validation_context or on: [:create, :custom_validation_context])

• :except_on - Specifies the contexts where this validation is not active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. except: :create or except_on: :custom_validation_context or except_on: [:create, :custom_validation_context])

• :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.

• :allow_nil - Skip validation if the attribute is nil.

• :allow_blank - Skip validation if the attribute is blank.

• :strict - If the :strict option is set to true will raise ActiveModel::StrictValidationFailed instead of adding the error. :strict option can also be set to any other exception.

Example:

validates :password, presence: true, confirmation: true, if: :password_required?
validates :token, length: { is: 24 }, strict: TokenLengthException

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

validates :password, presence: { if: :password_required?, message: 'is forgotten.' }, confirmation: true

This method is used to define validations that cannot be corrected by end users and are 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 the validation itself.

class Person
  include ActiveModel::Validations

  attr_accessor :name
  validates! :name, presence: true
end

person = Person.new
person.name = ''
person.valid?
# => ActiveModel::StrictValidationFailed: Name can't be blank

Validates each attribute against a block.

class Person
  include ActiveModel::Validations

  attr_accessor :first_name, :last_name

  validates_each :first_name, :last_name, allow_blank: true do |record, attr, value|
    record.errors.add attr, "starts with z." if value.start_with?("z")
  end
end

Options:

• :on - Specifies the contexts where this validation is active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. on: :create or on: :custom_validation_context or on: [:create, :custom_validation_context])

• :except_on - Specifies the contexts where this validation is not active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. except: :create or except_on: :custom_validation_context or except_on: [:create, :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.

Passes the record off to the class or classes specified and allows them to add errors based on more complex conditions.

class Person
  include ActiveModel::Validations
  validates_with MyValidator
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    if some_complex_logic
      record.errors.add :base, 'This record is invalid'
    end
  end

  private
    def some_complex_logic
      # ...
    end
end

You may also pass it multiple classes, like so:

class Person
  include ActiveModel::Validations
  validates_with MyValidator, MyOtherValidator, on: :create
end

There is no default error message for validates_with. You must manually add errors to the record’s errors collection in the validator class.

To implement the validate method, you must have a record parameter defined, which is the record to be validated.

Configuration options:

• :on - Specifies the contexts where this validation is active. Runs in all validation contexts by default nil. You can pass a symbol or an array of symbols. (e.g. on: :create or on: :custom_validation_context or on: [:create, :custom_validation_context])

• :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.

• :strict - Specifies whether validation should be strict. See ActiveModel::Validations#validates! for more information.

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.

class Person
  include ActiveModel::Validations

  validates_with MyValidator
  validates_with OtherValidator, on: :create
  validates_with StrictValidator, strict: true
end

Person.validators
# => [
#      #<MyValidator:0x007fbff403e808 @options={}>,
#      #<OtherValidator:0x007fbff403d930 @options={on: :create}>,
#      #<StrictValidator:0x007fbff3204a30 @options={strict:true}>
#    ]

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

class Person
  include ActiveModel::Validations

  attr_accessor :name, :age

  validates_presence_of :name
  validates_inclusion_of :age, in: 0..99
end

Person.validators_on(:name)
# => [
#       #<ActiveModel::Validations::PresenceValidator:0x007fe604914e60 @attributes=[:name], @options={}>,
#    ]