feat(correlation): don't generate Event-Id if it's provided (#61)

* Don't generate EventID if it's provided

* Fix typo

* Update extension/correlation/eventstore.go

Co-authored-by: Danilo Cianfrone <danilocianfr@gmail.com>

Co-authored-by: Konstantin Alexandrov <kale@hellofresh.com>
Co-authored-by: Danilo Cianfrone <danilocianfr@gmail.com>

Author: 3 people

CHANGELOG.md

@@ -10,7 +10,7 @@ project adheres to [Semantic Versioning](https://semver.org/).
 - An option to override Event appending logic in Postgres EventStore implementation. 
 
 ### Changed
-- ...
+- Existing `Event-Id` value in Event Metadata does not get overwritten in correlation.EventStoreWrapper.
 
 ### Deprecated
 - ...

extension/correlation/eventstore.go

@@ -53,7 +53,10 @@ func (esw EventStoreWrapper) Append(
 	}
 
 	for i, event := range events {
-		eventID := esw.Generator()
+		eventID, ok := event.Metadata[EventIDKey].(string)
+		if !ok {
+			eventID = esw.Generator()
+		}
 
 		event.Metadata = event.Metadata.
 			With(EventIDKey, eventID).

extension/correlation/eventstore_test.go

@@ -42,12 +42,15 @@ func TestEventStoreWrapper(t *testing.T) {
 		Name: "my-instance",
 	}
 
+	metadataWithEventID := eventually.Metadata{}.With(correlation.EventIDKey, "abc123")
+
 	_, err := correlatedEventStore.Append(
 		ctx,
 		streamID,
 		eventstore.VersionCheck(0),
 		eventually.Event{Payload: internal.StringPayload("my-first-event")},
 		eventually.Event{Payload: internal.StringPayload("my-second-event")},
+		eventually.Event{Payload: internal.StringPayload("my-third-event"), Metadata: metadataWithEventID},
 	)
 
 	if !assert.NoError(t, err) {
@@ -60,9 +63,9 @@ func TestEventStoreWrapper(t *testing.T) {
 	})
 
 	assert.NoError(t, err)
-	assert.Len(t, events, 2)
+	assert.Len(t, events, 3)
 
-	firstEvent, secondEvent := events[0].Event, events[1].Event
+	firstEvent, secondEvent, thirdEvent := events[0].Event, events[1].Event, events[2].Event
 
 	correlation1, ok := correlation.Message(firstEvent).CorrelationID()
 	assert.True(t, ok)
@@ -86,4 +89,11 @@ func TestEventStoreWrapper(t *testing.T) {
 	assert.Equal(t, causation1, causation2)
 	assert.Equal(t, correlation1, causation1)
 	assert.NotEqual(t, id1, id2)
+
+	assert.Equal(t, extractEventID(metadataWithEventID), extractEventID(thirdEvent.Metadata))
+}
+
+func extractEventID(m eventually.Metadata) string {
+	eventID, _ := m[correlation.EventIDKey].(string)
+	return eventID
 }