Add support for customizing fields

lib/active_model/serializer.rb

@@ -246,12 +246,16 @@ module ActiveModel
         self._attributes = _attributes.dup
 
         attrs.each do |attr|
-          self._attributes[attr] = attr
+          attribute attr
         end
       end
 
       def attribute(attr, options={})
         self._attributes = _attributes.merge(attr => options[:key] || attr)
+
+        unless method_defined?(attr)
+          class_eval "def #{attr}() object.read_attribute_for_serialization(:#{attr}) end", __FILE__, __LINE__
+        end
       end
 
       def associate(klass, attrs) #:nodoc:
@@ -490,11 +494,15 @@ module ActiveModel
       hash = {}
 
       _attributes.each do |name,key|
-        hash[key] = @object.read_attribute_for_serialization(name)
+        hash[key] = read_attribute_for_serialization(name)
       end
 
       hash
     end
+
+    def read_attribute_for_serialization(name)
+      send name
+    end
   end
 end
 

test/serializer_test.rb

@@ -814,4 +814,58 @@ class SerializerTest < ActiveModel::TestCase
       ]
     }, actual)
   end
+
+  def test_can_customize_attributes
+    serializer = Class.new(ActiveModel::Serializer) do
+      attributes :title, :body
+
+      def title
+        object.title.upcase
+      end
+    end
+
+    klass = Class.new do
+      def read_attribute_for_serialization(name)
+        { :title => "New post!", :body => "First post body" }[name]
+      end
+
+      def title
+        read_attribute_for_serialization(:title)
+      end
+
+      def body
+        read_attribute_for_serialization(:body)
+      end
+    end
+
+    object = klass.new
+
+    actual = serializer.new(object, :root => :post).as_json
+
+    assert_equal({
+      :post => {
+        :title => "NEW POST!",
+        :body => "First post body"
+      }
+    }, actual)
+  end
+
+  def test_can_customize_attributes_with_read_attributes
+    serializer = Class.new(ActiveModel::Serializer) do
+      attributes :title, :body
+
+      def read_attribute_for_serialization(name)
+        { :title => "New post!", :body => "First post body" }[name]
+      end
+    end
+
+    actual = serializer.new(Object.new, :root => :post).as_json
+
+    assert_equal({
+      :post => {
+        :title => "New post!",
+        :body => "First post body"
+      }
+    }, actual)
+  end
 end