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.
COMPILABLE_REGEXP | = | /\A[a-zA-Z_]\w*[!?=]?\z/ |
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.
Source: show
# File activemodel/lib/active_model/attribute_methods.rb, line 379 def method_missing(method_id, *args, &block) method_name = method_id.to_s if match = match_attribute_method?(method_name) guard_private_attribute_method!(method_name, args) return __send__(match.target, match.attr_name, *args, &block) end super end
Source: show
# File activemodel/lib/active_model/attribute_methods.rb, line 392 def respond_to?(method, include_private_methods = false) if super return 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. return false elsif match_attribute_method?(method.to_s) return true end super 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
.
Source: show
# File activemodel/lib/active_model/attribute_methods.rb, line 406 def attribute_method?(attr_name) attributes.include?(attr_name) end