Active Model Validation Callbacks

Provides an interface for any class to have before_validation and after_validation callbacks.

First, include ActiveModel::Validations::Callbacks from the class you are creating:

class MyModel
  include ActiveModel::Validations::Callbacks

  before_validation :do_stuff_before_validation
  after_validation  :do_stuff_after_validation
end

Like other before_* callbacks if before_validation returns false then valid? will not be called.