[MODEL] Clean up getting attributes from as_indexed_json in update_document

Basically, flipping the relationship here should be enough: select based on
`changed_attributes` keys from the `as_indexed_json` Hash, not vice versa.

Related: elastic#166

Author: karmi

elasticsearch-model/lib/elasticsearch/model/indexing.rb

@@ -336,11 +336,7 @@ def delete_document(options={})
         def update_document(options={})
           if changed_attributes = self.instance_variable_get(:@__changed_attributes)
             attributes = if respond_to?(:as_indexed_json)
-              json = self.as_indexed_json
-              changed_attributes.inject({}) do |memo,(key,value)|
-                memo[key] = json[key] if json.keys.include? key
-                memo
-              end
+              self.as_indexed_json.select { |k,v| changed_attributes.keys.map(&:to_s).include? k.to_s }
             else
               changed_attributes
             end

elasticsearch-model/test/unit/indexing_test.rb

@@ -285,7 +285,7 @@ def as_indexed_json(options={})
         instance.instance_variable_set(:@__changed_attributes, {'foo' => 'B', 'bar' => 'D' })
 
         client.expects(:update).with do |payload|
-          assert_equal({'foo' => 'B'}, payload[:body][:doc])
+          assert_equal({:foo => 'B'}, payload[:body][:doc])
         end
 
         instance.expects(:client).returns(client)
@@ -300,10 +300,12 @@ def as_indexed_json(options={})
         client   = mock('client')
         instance = ::DummyIndexingModelWithCallbacksAndCustomAsIndexedJson.new
 
-        instance.instance_variable_set(:@__changed_attributes, {foo: {ru:'B'} })
+        instance.instance_variable_set(:@__changed_attributes, { 'foo' => { 'bar' => 'BAR'} })
+        # Overload as_indexed_json
+        instance.expects(:as_indexed_json).returns({ 'foo' => 'BAR' })
 
         client.expects(:update).with do |payload|
-          assert_equal({foo: 'B'}, payload[:body][:doc])
+          assert_equal({'foo' => 'BAR'}, payload[:body][:doc])
         end
 
         instance.expects(:client).returns(client)