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
# File activemodel/lib/active_model/attribute_methods.rb, line 467 def attribute_missing(match, *args, &block) __send__(match.target, match.attr_name, *args, &block) end
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 activemodel/lib/active_model/attribute_methods.rb, line 453 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
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 activemodel/lib/active_model/attribute_methods.rb, line 475 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
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
.
© 2004–2021 David Heinemeier Hansson
Licensed under the MIT License.