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Module: ActiveModel::AttributeMethods

Relationships & Source Files
Namespace Children
Modules:
ClassMethods
Extension / Inclusion / Inheritance Descendants
Included In:
Attributes, Dirty, ::ActiveRecord::AttributeMethods, ::ActiveRecord::AttributeMethods::Dirty, ::ActiveRecord::Base, ActiveRecord::InternalMetadata, ActiveRecord::SchemaMigration
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::ActiveSupport::Concern
Defined in: activemodel/lib/active_model/attribute_methods.rb,
activemodel/lib/active_model/attributes.rb

Overview

Provides a way to add prefixes and suffixes to your methods as well as handling the creation of ::ActiveRecord::Base-like class methods such as table_name.

The requirements to implement AttributeMethods are to:

  • include ActiveModel::AttributeMethods in your class.

  • Call each of its methods you want to add, such as attribute_method_suffix or attribute_method_prefix.

  • Call define_attribute_methods after the other methods are called.

  • Define the various generic _attribute methods that you have declared.

  • Define 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.

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

  def attributes
    { 'name' => @name }
  end

  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

Constant Summary

Class Method Summary

::ActiveSupport::Concern - Extended

append_features, class_methods, included

Instance Method Summary

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(method, *args, &block)

Allows access to the object attributes, which are held in the hash returned by attributes, as though they were first-class methods. So a Person class with a name attribute can for example use Person#name and Person#name= and never directly use the attributes hash – except for multiple assignments with ActiveRecord::Base#attributes=.

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.

[ GitHub ] 

  


# File 'activemodel/lib/active_model/attribute_methods.rb', line 425



def method_missing(method, *args, &block)
  if respond_to_without_attributes?(method, true)
    super
  else
    match = matched_attribute_method(method.to_s)
    match ? attribute_missing(match, *args, &block) : super
  end
end


  







DSL Calls




included

  [ GitHub ]


  


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73
74

  


# File 'activemodel/lib/active_model/attribute_methods.rb', line 71



included do
  class_attribute :attribute_aliases, instance_writer: false, default: {}
  class_attribute :attribute_method_matchers, instance_writer: false, default: [ ClassMethods::AttributeMethodMatcher.new ]
end


  







Instance Method Details



  

    #attribute_missing(match, *args, &block)  
  



  

    

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 tell attribute_missing to dispatch the attribute. This method can be overloaded to customize the behavior.


  



  [ GitHub ]


  

  


# File 'activemodel/lib/active_model/attribute_methods.rb', line 438



def attribute_missing(match, *args, &block)
  __send__(match.target, match.attr_name, *args, &block)
end


  








  

    #respond_to?(method, include_private_methods = false)  ⇒ Boolean 
  



  

    
  





  


  [ GitHub ]


  

  


# File 'activemodel/lib/active_model/attribute_methods.rb', line 446



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
    !matched_attribute_method(method.to_s).nil?
  end
end


  








  

    #respond_to_without_attributes?  
  



  

    

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


  



  [ GitHub ]


  

  


# File 'activemodel/lib/active_model/attribute_methods.rb', line 445



alias :respond_to_without_attributes? :respond_to?