validates_inclusion_of

Validates whether the value of the specified attribute is available in a particular enumerable object.

class Person < ActiveRecord::Base
  validates_inclusion_of :gender, in: %w( m f )
  validates_inclusion_of :age, in: 0..99
  validates_inclusion_of :format, in: %w( jpg gif png ), message: "extension %{value} is not included in the list"
  validates_inclusion_of :states, in: ->(person) { STATES[person.country] }
  validates_inclusion_of :karma, in: :available_karmas
end

Configuration options:

• :in - An enumerable object of available items. This can be supplied as a proc, lambda or symbol which returns an enumerable. If the enumerable is a numerical range the test is performed with Range#cover?, otherwise with include?. When using a proc or lambda the instance under validation is passed as an argument.

• :within - A synonym(or alias) for :in

• :message - Specifies a custom error message (default is: “is not included in the list”).

There is also a list of default options supported by every validator: :if, :unless, :on, :allow_nil, :allow_blank, and :strict. See ActiveModel::Validation#validates for more information