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:
include ActiveModel::AttributeMethods in your object
Call each Attribute Method module method 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
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.
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
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.
# 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
# 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
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.
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