allow multiple handlers for the same event within one event group

Author: roblaszczak

components/cqrs/event_processor_group.go

@@ -133,6 +133,10 @@ func NewEventGroupProcessorWithConfig(router *message.Router, config EventGroupP
 //
 // Compared to AddHandlers, AddHandlersGroup allows to have multiple handlers that share the same subscriber instance.
 //
+// It's allowed to have multiple handlers for the same event type in one group, but we recommend to not do that.
+// Please keep in mind that those handlers will be processed within the same message.
+// If first handler succeeds and the second fails, the message will be re-delivered and the first will be re-executed.
+//
 // Handlers group needs to be unique within the EventProcessor instance.
 //
 // Handler group name is used as handler's name in router.
@@ -203,6 +207,8 @@ func (p EventGroupProcessor) routerHandlerGroupFunc(handlers []GroupEventHandler
 	return func(msg *message.Message) error {
 		messageEventName := p.config.Marshaler.NameFromMessage(msg)
 
+		handledAnyEvent := false
+
 		for _, handler := range handlers {
 			initEvent := handler.NewEvent()
 			expectedEventName := p.config.Marshaler.Name(initEvent)
@@ -249,6 +255,9 @@ func (p EventGroupProcessor) routerHandlerGroupFunc(handlers []GroupEventHandler
 				return err
 			}
 
+			handledAnyEvent = true
+		}
+		if handledAnyEvent {
 			return nil
 		}
 

components/cqrs/event_processor_group_test.go

@@ -300,21 +300,27 @@ func TestEventProcessor_handler_group(t *testing.T) {
 		},
 	}
 
-	handler1Calls := 0
-	handler2Calls := 0
+	var handlersCalls []int
 
 	handlers := []cqrs.GroupEventHandler{
 		cqrs.NewGroupEventHandler(func(ctx context.Context, event *TestEvent) error {
 			assert.EqualValues(t, event1, event)
 
-			handler1Calls++
+			handlersCalls = append(handlersCalls, 1)
 
 			return nil
 		}),
 		cqrs.NewGroupEventHandler(func(ctx context.Context, event *AnotherTestEvent) error {
 			assert.EqualValues(t, event2, event)
 
-			handler2Calls++
+			handlersCalls = append(handlersCalls, 2)
+
+			return nil
+		}),
+		cqrs.NewGroupEventHandler(func(ctx context.Context, event *AnotherTestEvent) error {
+			assert.EqualValues(t, event2, event)
+
+			handlersCalls = append(handlersCalls, 3)
 
 			return nil
 		}),
@@ -382,8 +388,7 @@ func TestEventProcessor_handler_group(t *testing.T) {
 		t.Fatal("message 2 not acked")
 	}
 
-	assert.Equal(t, 1, handler1Calls)
-	assert.Equal(t, 1, handler2Calls)
+	assert.Equal(t, []int{1, 2, 3}, handlersCalls)
 }
 
 func TestEventGroupProcessor_original_msg_set_to_ctx(t *testing.T) {