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:
-
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.
Constants
- CALL_COMPILABLE_REGEXP
- NAME_COMPILABLE_REGEXP
Public Instance Methods
#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
.
Protected Instance Methods
# 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
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
# File lib/active_model/attribute_methods.rb, line 448 def missing_attribute(attr_name, stack) raise ActiveModel::MissingAttributeError, "missing attribute: #{attr_name}", stack end