module ActiveModel::Validations::Callbacks::ClassMethods   
        
        Public instance methods
Defines a callback that will get called right after validation.
class Person
  include ActiveModel::Validations
  include ActiveModel::Validations::Callbacks
  attr_accessor :name, :status
  validates_presence_of :name
  after_validation :set_status
  private
    def set_status
      self.status = errors.empty?
    end
end
person = Person.new
person.name = ''
person.valid? # => false
person.status # => false
person.name = 'bob'
person.valid? # => true
person.status # => true
Source code GitHub
# File activemodel/lib/active_model/validations/callbacks.rb, line 88
def after_validation(*args, &block)
  options = args.extract_options!
  options = options.dup
  options[:prepend] = true
  set_options_for_callback(options)
  set_callback(:validation, :after, *args, options, &block)
end
            Defines a callback that will get called right before validation.
class Person
  include ActiveModel::Validations
  include ActiveModel::Validations::Callbacks
  attr_accessor :name
  validates_length_of :name, maximum: 6
  before_validation :remove_whitespaces
  private
    def remove_whitespaces
      name.strip!
    end
end
person = Person.new
person.name = '  bob  '
person.valid? # => true
person.name   # => "bob"
Source code GitHub
# File activemodel/lib/active_model/validations/callbacks.rb, line 55
def before_validation(*args, &block)
  options = args.extract_options!
  set_options_for_callback(options)
  set_callback(:validation, :before, *args, options, &block)
end