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 ), :message => "woah! what are you then!??!!"
  validates_inclusion_of :age, :in => 0..99
  validates_inclusion_of :format, :in => %w( jpg gif png ), :message => "extension %s is not included in the list"
end

Configuration options:

• in - An enumerable object of available items
• message - Specifies a customer error message (default is: "is not included in the list")
• allow_nil - If set to true, skips this validation if the attribute is null (default is: false)
• allow_blank - If set to true, skips this validation if the attribute is blank (default is: false)
• if - Specifies a method, proc or string to call to determine if the validation should occur (e.g. :if => :allow_validation, or :if => Proc.new { |user| user.signup_step > 2 }). The method, proc or string should return or evaluate to a true or false value.
• unless - Specifies a method, proc or string to call to determine if the validation should not occur (e.g. :unless => :skip_validation, or :unless => Proc.new { |user| user.signup_step <= 2 }). The method, proc or string should return or evaluate to a true or false value.

Source Code

# File active_record/validations.rb, line 748
def validates_inclusion_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:inclusion], :on => :save }
  configuration.update(attr_names.extract_options!)

  enum = configuration[:in] || configuration[:within]

  raise(ArgumentError, "An object with the method include? is required must be supplied as the :in option of the configuration hash") unless enum.respond_to?("include?")

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message] % value) unless enum.include?(value)
  end
end