[MODEL] Avoid making an update when no attributes are changed (elastic#762)

Closes elastic#743

Author: nilbus

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

@@ -397,7 +397,7 @@ def delete_document(options={})
         # @see http://rubydoc.info/gems/elasticsearch-api/Elasticsearch/API/Actions:update
         #
         def update_document(options={})
-          if attributes_in_database = self.instance_variable_get(:@__changed_model_attributes)
+          if attributes_in_database = self.instance_variable_get(:@__changed_model_attributes).presence
             attributes = if respond_to?(:as_indexed_json)
               self.as_indexed_json.select { |k,v| attributes_in_database.keys.map(&:to_s).include? k.to_s }
             else

elasticsearch-model/test/unit/indexing_test.rb

@@ -176,6 +176,19 @@ def changes_to_save
         end
       end
 
+      class ::DummyIndexingModelWithNoChanges
+        extend  Elasticsearch::Model::Indexing::ClassMethods
+        include Elasticsearch::Model::Indexing::InstanceMethods
+
+        def self.before_save(&block)
+          (@callbacks ||= {})[block.hash] = block
+        end
+
+        def changes_to_save
+          {}
+        end
+      end
+
       class ::DummyIndexingModelWithCallbacksAndCustomAsIndexedJson
         extend  Elasticsearch::Model::Indexing::ClassMethods
         include Elasticsearch::Model::Indexing::InstanceMethods
@@ -393,6 +406,26 @@ def changes
         instance.update_document
       end
 
+      should "index instead of update when nothing was changed" do
+        client   = mock('client')
+        instance = ::DummyIndexingModelWithNoChanges.new
+
+        # Set the fake `changes` hash
+        instance.instance_variable_set(:@__changed_model_attributes, {})
+        # Overload as_indexed_json for running index
+        instance.expects(:as_indexed_json).returns({ 'foo' => 'BAR' })
+
+        client.expects(:index)
+        client.expects(:update).never
+
+        instance.expects(:client).returns(client)
+        instance.expects(:index_name).returns('foo')
+        instance.expects(:document_type).returns('bar')
+        instance.expects(:id).returns('1')
+
+        instance.update_document({})
+      end
+
       should "update only the specific attributes" do
         client   = mock('client')
         instance = ::DummyIndexingModelWithCallbacks.new