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Active Model Validator

A simple base class that can be used along with ActiveModel::Validations::ClassMethods#validates_with

class Person
  include ActiveModel::Validations
  validates_with MyValidator
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    if some_complex_logic
      record.errors[:base] = "This record is invalid"
    end
  end

  private
    def some_complex_logic
      # ...
    end
end

Any class that inherits from ActiveModel::Validator must implement a method called validate which accepts a record.

class Person
  include ActiveModel::Validations
  validates_with MyValidator
end

class MyValidator < ActiveModel::Validator
  def validate(record)
    record # => The person instance being validated
    options # => Any non-standard options passed to validates_with
  end
end

To cause a validation error, you must add to the record's errors directly from within the validators message.

class MyValidator < ActiveModel::Validator
  def validate(record)
    record.errors.add :base, "This is some custom error message"
    record.errors.add :first_name, "This is some complex validation"
    # etc...
  end
end

To add behavior to the initialize method, use the following signature:

class MyValidator < ActiveModel::Validator
  def initialize(options)
    super
    @my_custom_field = options[:field_name] || :first_name
  end
end

Note that the validator is initialized only once for the whole application life cycle, and not on each validation run.

The easiest way to add custom validators for validating individual attributes is with the convenient ActiveModel::EachValidator.

class TitleValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    record.errors.add attribute, 'must be Mr., Mrs., or Dr.' unless %w(Mr. Mrs. Dr.).include?(value)
  end
end

This can now be used in combination with the validates method (see ActiveModel::Validations::ClassMethods.validates for more on this).

class Person
  include ActiveModel::Validations
  attr_accessor :title

  validates :title, presence: true
end

It can be useful to access the class that is using that validator when there are prerequisites such as an attr_accessor being present. This class is accessible via +options+ in the constructor. To setup your validator override the constructor.

class MyValidator < ActiveModel::Validator
  def initialize(options={})
    super
    options[:class].send :attr_accessor, :custom_attribute
  end
end
Methods
K
N
V
Attributes
[R] options
Class Public methods
kind()

Returns the kind of the validator.

PresenceValidator.kind   # => :presence
UniquenessValidator.kind # => :uniqueness
# File activemodel/lib/active_model/validator.rb, line 102
def self.kind
  @kind ||= name.split('::').last.underscore.sub(/_validator$/, '').to_sym unless anonymous?
end
new(options = {})

Accepts options that will be made available through the options reader.

# File activemodel/lib/active_model/validator.rb, line 107
def initialize(options = {})
  @options  = options.except(:class).freeze
  deprecated_setup(options)
end
Instance Public methods
kind()

Returns the kind for this validator.

PresenceValidator.new.kind   # => :presence
UniquenessValidator.new.kind # => :uniqueness
# File activemodel/lib/active_model/validator.rb, line 116
def kind
  self.class.kind
end
validate(record)

Override this method in subclasses with validation logic, adding errors to the records errors array where necessary.

# File activemodel/lib/active_model/validator.rb, line 122
def validate(record)
  raise NotImplementedError, "Subclasses must implement a validate(record) method."
end