validates_with

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 :instance_validations

    def instance_validations
      validates_with MyValidator
    end
  end

Please consult the class method documentation for more information on creating your own validator.

You may also pass it multiple classes, like so:

  class Person
    include ActiveModel::Validations

    validates :instance_validations, :on => :create

    def instance_validations
      validates_with MyValidator, MyOtherValidator
    end
  end

Standard configuration options (:on, :if and :unless), which are available on the class version of validates_with, should instead be placed on the validates method as these are applied and tested in the callback

If you pass any additional configuration options, they will be passed to the class and available as options, please refer to the class version of this method for more information