module ActiveModel::AttributeMethods

Active Model Attribute Methods

ActiveModel::AttributeMethods provides a way to add prefixes and suffixes to your methods as well as handling the creation of Active Record like class methods such as table_name.

The requirements to implement ActiveModel::AttributeMethods are to:

A minimal implementation could be:

class Person
  include ActiveModel::AttributeMethods

  attribute_method_affix  :prefix => 'reset_', :suffix => '_to_default!'
  attribute_method_suffix '_contrived?'
  attribute_method_prefix 'clear_'
  define_attribute_methods ['name']

  attr_accessor :name

  private

  def attribute_contrived?(attr)
    true
  end

  def clear_attribute(attr)
    send("#{attr}=", nil)
  end

  def reset_attribute_to_default!(attr)
    send("#{attr}=", "Default Name")
  end
end

Note that whenever you include ActiveModel::AttributeMethods in your class, it requires you to implement an attributes method which returns a hash with each attribute name in your model as hash key and the attribute value as hash value.

Hash keys must be strings.

Constants

CALL_COMPILABLE_REGEXP
NAME_COMPILABLE_REGEXP

Public Instance Methods

attribute_missing(match, *args, &block) click to toggle source

#attribute_missing is like #method_missing, but for attributes. When #method_missing is called we check to see if there is a matching attribute method. If so, we call #attribute_missing to dispatch the attribute. This method can be overloaded to customise the behaviour.

# File lib/active_model/attribute_methods.rb, line 415
def attribute_missing(match, *args, &block)
  __send__(match.target, match.attr_name, *args, &block)
end
method_missing(method, *args, &block) click to toggle source

Allows access to the object attributes, which are held in the @attributes hash, as though they were first-class methods. So a Person class with a name attribute can use Person#name and Person#name= and never directly use the attributes hash – except for multiple assigns with ActiveRecord#attributes=. A Milestone class can also ask Milestone#completed? to test that the completed attribute is not nil or 0.

It's also possible to instantiate related objects, so a Client class belonging to the clients table with a master_id foreign key can instantiate master through Client#master.

Calls superclass method
# File lib/active_model/attribute_methods.rb, line 402
def method_missing(method, *args, &block)
  if respond_to_without_attributes?(method, true)
    super
  else
    match = match_attribute_method?(method.to_s)
    match ? attribute_missing(match, *args, &block) : super
  end
end
respond_to?(method, include_private_methods = false) click to toggle source
Calls superclass method
# File lib/active_model/attribute_methods.rb, line 423
def respond_to?(method, include_private_methods = false)
  if super
    true
  elsif !include_private_methods && super(method, true)
    # If we're here then we haven't found among non-private methods
    # but found among all methods. Which means that the given method is private.
    false
  else
    !match_attribute_method?(method.to_s).nil?
  end
end
respond_to_without_attributes?(method, include_private_methods = false)

A Person object with a name attribute can ask person.respond_to?(:name), person.respond_to?(:name=), and person.respond_to?(:name?) which will all return true.

Alias for: respond_to?

Protected Instance Methods

attribute_method?(attr_name) click to toggle source
# File lib/active_model/attribute_methods.rb, line 436
def attribute_method?(attr_name)
  respond_to_without_attributes?(:attributes) && attributes.include?(attr_name)
end

Private Instance Methods

match_attribute_method?(method_name) click to toggle source

Returns a struct representing the matching attribute method. The struct's attributes are prefix, base and suffix.

# File lib/active_model/attribute_methods.rb, line 443
def match_attribute_method?(method_name)
  match = self.class.send(:attribute_method_matcher, method_name)
  match && attribute_method?(match.attr_name) ? match : nil
end
missing_attribute(attr_name, stack) click to toggle source
# File lib/active_model/attribute_methods.rb, line 448
def missing_attribute(attr_name, stack)
  raise ActiveModel::MissingAttributeError, "missing attribute: #{attr_name}", stack
end