Add support for overriding associations, mostly used for authorization

activemodel/lib/active_model/serializer.rb

@@ -41,6 +41,10 @@ module ActiveModel
       def associate(klass, attrs)
         options = attrs.extract_options!
         self._associations += attrs.map do |attr|
+          unless method_defined?(attr)
+            class_eval "def #{attr}() object.#{attr} end", __FILE__, __LINE__
+          end
+
           options[:serializer] ||= const_get("#{attr.to_s.camelize}Serializer")
           klass.new(attr, options)
         end
@@ -79,7 +83,7 @@ module ActiveModel
       hash = attributes
 
       _associations.each do |association|
-        associated_object = object.send(association.name)
+        associated_object = send(association.name)
         hash[association.name] = association.serialize(associated_object, scope)
       end
 

activemodel/test/cases/serializer_test.rb

@@ -174,4 +174,30 @@ class SerializerTest < ActiveModel::TestCase
       }
     }, json)
   end
+
+  def test_overridden_associations
+    author_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :first_name
+    end
+
+    blog_serializer = Class.new(ActiveModel::Serializer) do
+      const_set(:PersonSerializer, author_serializer)
+      has_one :person
+
+      def person
+        object.author
+      end
+    end
+
+    user = User.new
+    blog = Blog.new
+    blog.author = user
+
+    json = blog_serializer.new(blog, user).as_json
+    assert_equal({
+      :person => {
+        :first_name => "Jose"
+      }
+    }, json)
+  end
 end