Ignore old/duplicate events in projector

looplab · Dec 7, 2020 · 9c34447 · 9c34447
1 parent 82599db
commit 9c34447
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Showing 2 changed files with 15 additions and 0 deletions.
diff --git a/eventhandler/projector/eventhandler.go b/eventhandler/projector/eventhandler.go
@@ -124,6 +124,11 @@ func (h *EventHandler) HandleEvent(ctx context.Context, event eh.Event) error {
 
 	// The entity should be one version behind the event.
 	if entity, ok := entity.(eh.Versionable); ok {
+		// Ignore old/duplicate events.
+		if entity.AggregateVersion() >= event.Version() {
+			return nil
+		}
+
 		if entity.AggregateVersion()+1 != event.Version() {
 			return Error{
 				Err:       eh.ErrIncorrectEntityVersion,

diff --git a/eventhandler/projector/eventhandler_test.go b/eventhandler/projector/eventhandler_test.go
@@ -99,6 +99,11 @@ func TestEventHandler_UpdateModel(t *testing.T) {
 	if repo.Entity != projector.newEntity {
 		t.Error("the new entity should be correct:", repo.Entity)
 	}
+
+	// Handle event again, should be a no-op.
+	if err := handler.HandleEvent(ctx, event); err != nil {
+		t.Error("there shoud be no error:", err)
+	}
 }
 
 func TestEventHandler_UpdateModelWithVersion(t *testing.T) {
@@ -137,6 +142,11 @@ func TestEventHandler_UpdateModelWithVersion(t *testing.T) {
 	if repo.Entity != projector.newEntity {
 		t.Error("the new entity should be correct:", repo.Entity)
 	}
+
+	// Handle event again, should be a no-op.
+	if err := handler.HandleEvent(ctx, event); err != nil {
+		t.Error("there shoud be no error:", err)
+	}
 }
 
 func TestEventHandler_UpdateModelWithEventsOutOfOrder(t *testing.T) {