Module: ActiveModel::AttributeMethods

Extended by:

ActiveSupport::Concern

Included in:

Attributes, Dirty

Defined in:

lib/active_model/attributes.rb,
lib/active_model/attribute_methods.rb

Overview

Active Model Attribute Methods

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 ActiveModel::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

Defined Under Namespace

Modules: ClassMethods

Constant Summary

AttrNames =

Module.new {
  def self.set_name_cache(name, value)
    const_name = "ATTR_#{name}"
    unless const_defined? const_name
      const_set const_name, value.dup.freeze
    end
  end
}

NAME_COMPILABLE_REGEXP =

/\A[a-zA-Z_]\w*[!?=]?\z/

CALL_COMPILABLE_REGEXP =

/\A[a-zA-Z_]\w*[!?]?\z/

Instance Method Summary

• #attribute_missing(match, *args, &block) ⇒ Object

  attribute_missing is like method_missing, but for attributes.

• #method_missing(method, *args, &block) ⇒ Object

  Allows access to the object attributes, which are held in the hash returned by attributes, as though they were first-class methods.

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

  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.

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(method, *args, &block) ⇒ Object

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.

# File '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

Instance Method Details

#attribute_missing(match, *args, &block) ⇒ Object

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.

# File '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

Returns:

• (Boolean)

# File '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? ⇒ Object

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.

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

alias :respond_to_without_attributes? :respond_to?