type_key_name should be "_type" for ManyAssociation and OneAssociatio…

…n, only "#{as}_type" for BelongsToAssociation

lib/mongo_mapper/plugins/associations/base.rb

@@ -40,7 +40,7 @@ def embeddable?
         end
 
         def type_key_name
-          "#{as}_type"
+          "_type"
         end
 
         def as

lib/mongo_mapper/plugins/associations/belongs_to_association.rb

@@ -3,6 +3,10 @@ module MongoMapper
   module Plugins
     module Associations
       class BelongsToAssociation < SingleAssociation
+        def type_key_name
+          "#{as}_type"
+        end
+
         def embeddable?
           false
         end

lib/mongo_mapper/plugins/associations/many_association.rb

@@ -8,10 +8,6 @@ def class_name
           @class_name ||= options[:class_name] || name.to_s.singularize.camelize
         end
 
-        def type_key_name
-          "_type"
-        end
-
         # hate this, need to revisit
         def proxy_class
           @proxy_class ||= if klass.embeddable?

test/unit/associations/test_one_association.rb

@@ -4,6 +4,12 @@
 class OneAssociationTest < Test::Unit::TestCase
   include MongoMapper::Plugins::Associations
 
+  context "type_key_name" do
+    should "be _type" do
+      OneAssociation.new(:foo).type_key_name.should == '_type'
+    end
+  end
+
   context "embeddable?" do
     should "be true if class is embeddable" do
       base = OneAssociation.new(:media)