Generate id method on Ruby 1.8.

Because object_id and id went through some flux, it's best to tell 1.8
specifically what we mean.

Closes #127.

CHANGELOG.md

@@ -1,5 +1,8 @@
 # unreleased
 
+* On Ruby 1.8, we now generate an `id` method that properly serializes `id`
+  columns. See issue #127 for more.
+
 * Add an alias for `scope` method to be the name of the context. By default
   this is `current_user`. The name is automatically set when using
   `serialization_scope` in the controller.

lib/generators/serializer/serializer_generator.rb

@@ -12,9 +12,10 @@ module Rails
         template 'serializer.rb', File.join('app/serializers', class_path, "#{file_name}_serializer.rb")
       end
 
-      # hook_for :test_framework
-
       private
+      def generate_id_method
+        RUBY_VERSION =~ /1\.8/
+      end
 
       def attributes_names
         [:id] + attributes.select { |attr| !attr.reference? }.map { |a| a.name.to_sym }

lib/generators/serializer/templates/serializer.rb

@@ -4,5 +4,16 @@ class <%= class_name %>Serializer < <%= parent_class_name %>
 <% association_names.each  do |attribute| -%>
   has_one :<%= attribute %>
 <% end  -%>
+<% if  generate_id_method %>
+
+  # due to the difference between 1.8 and 1.9 with respect to #id and
+  # #object_id, we reccomend that if you wish to serialize id columns, you
+  # do this. Feel free to remove this if you don't feel that it's appropriate.
+  # 
+  # For more: https://github.com/rails-api/active_model_serializers/issues/127
+  def id
+    object.read_attribute_for_serialization(:id)
+  end
+<% end  -%>
 end
 <% end  -%>

test/generators_test.rb

@@ -36,6 +36,18 @@ class SerializerGeneratorTest < Rails::Generators::TestCase
     Object.send :remove_const, :ApplicationSerializer
   end
 
+  def test_serializer_gets_id
+    run_generator
+
+    assert_file "app/serializers/account_serializer.rb" do |content|
+      if RUBY_VERSION =~ /1.8/
+        assert_match    /def id/, content
+      else
+        assert_no_match /def id/, content
+      end
+    end
+  end
+
   # def test_uses_namespace_application_serializer_if_one_exists
   #   Object.const_set(:SerializerNamespace, Module.new)
   #   SerializerNamespace.const_set(:ApplicationSerializer, Class.new)
@@ -66,6 +78,8 @@ class SerializerGeneratorTest < Rails::Generators::TestCase
 
   def test_with_no_attributes_does_not_add_extra_space
     run_generator ["account"]
-    assert_file "app/serializers/account_serializer.rb", /class AccountSerializer < ActiveModel::Serializer\n  attributes :id\nend/
+    assert_file "app/serializers/account_serializer.rb" do |content|
+      assert_no_match /\n\nend/, content
+    end
   end
 end