Add an attribute_missing method to ActiveModel::AttributeMethods.

This can be overloaded by implementors if necessary.

activemodel/lib/active_model/attribute_methods.rb

@@ -362,7 +362,7 @@ module ActiveModel
         class AttributeMethodMatcher
           attr_reader :prefix, :suffix, :method_missing_target
 
-          AttributeMethodMatch = Struct.new(:target, :attr_name)
+          AttributeMethodMatch = Struct.new(:target, :attr_name, :method_name)
 
           def initialize(options = {})
             options.symbolize_keys!
@@ -384,7 +384,7 @@ module ActiveModel
 
           def match(method_name)
             if @regex =~ method_name
-              AttributeMethodMatch.new(method_missing_target, $2)
+              AttributeMethodMatch.new(method_missing_target, $2, method_name)
             else
               nil
             end
@@ -416,15 +416,18 @@ module ActiveModel
         super
       else
         match = match_attribute_method?(method.to_s)
-
-        if match
-          __send__(match.target, match.attr_name, *args, &block)
-        else
-          super
-        end
+        match ? attribute_missing(match, *args, &block) : super
       end
     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 call
+    # attribute_missing to dispatch the attribute. This method can be overloaded to
+    # customise the behaviour.
+    def attribute_missing(match, *args, &block)
+      __send__(match.target, match.attr_name, *args, &block)
+    end
+
     # A Person object with a name attribute can ask <tt>person.respond_to?(:name)</tt>,
     # <tt>person.respond_to?(:name=)</tt>, and <tt>person.respond_to?(:name?)</tt>
     # which will all return +true+.

activemodel/test/cases/attribute_methods_test.rb

@@ -187,4 +187,19 @@ class AttributeMethodsTest < ActiveModel::TestCase
     assert m.respond_to?(:protected_method)
     assert m.respond_to?(:protected_method, true)
   end
+
+  test 'should use attribute_missing to dispatch a missing attribute' do
+    m = ModelWithAttributes2.new
+    m.attributes = { 'foo' => 'bar' }
+
+    def m.attribute_missing(match, *args, &block)
+      match
+    end
+
+    match = m.foo_test
+
+    assert_equal 'foo',            match.attr_name
+    assert_equal 'attribute_test', match.target
+    assert_equal 'foo_test',       match.method_name
+  end
 end