module ActiveModel::Validations::HelperMethods

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

reserved").
* :message - Specifies a custom error message (default is: "is
Range#cover?, otherwise with include?.
* :within - A synonym(or alias) for :in
using a proc or lambda the instance under validation is passed as an argument.
is performed with Range#cover?, otherwise with include?. When
enumerable. If the enumerable is a numerical, time or datetime range the test
be part of. This can be supplied as a proc, lambda or symbol which returns an
* :in - An enumerable object of items that the value shouldn't
Configuration options:

end
validates_exclusion_of :karma, in: :reserved_karmas
message: 'should not be the same as your username or first name'
validates_exclusion_of :password, in: ->(person) { [person.username, person.first_name] },
validates_exclusion_of :format, in: %w( mov avi ), message: "extension %{value} is not allowed"
validates_exclusion_of :age, in: 30..60, message: 'This site is only for under 30 and over 60'
validates_exclusion_of :username, in: %w( admin superuser ), message: "You don't belong here"
class Person < ActiveRecord::Base

particular enumerable object.
Validates that the value of the specified attribute is not in a

def validates_exclusion_of(*attr_names)
  validates_with ExclusionValidator, _merge_attributes(attr_names)
end