JAMES-2433 Implement EventStore for a JPA backend #2452

amichair · 2024-10-15T09:38:19Z

This is just a rough draft and not ready to merge yet, but since I have no previous experience with Scala or Reactive Streams or Guice or this event api or its usages, if anyone could help in improving and finalizing this, I think we can get this done :-)

chibenwa

Thanks, this is a cool first shot at it!

I did do a few comments to polish the code here.

Next steps would be to wire the event store into existing app and expose features relying on event sourcing onto the same applications.

chibenwa · 2024-10-15T12:18:48Z

...ent-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/JPAEventStore.java

+            EventStoreFailedException esfe = new EventStoreFailedException("Unable to add events");
+            esfe.initCause(e);
+            throw esfe;


Suggested change

EventStoreFailedException esfe = new EventStoreFailedException("Unable to add events");

esfe.initCause(e);

throw esfe;

throw new EventStoreFailedException("Unable to add events", e);

Mutability can be avoided

That's what I intended to do, but this exception doesn't support a cause parameter... I left the scala api part alone for now.

chibenwa · 2024-10-15T12:24:07Z

...ent-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/JPAEventStore.java

+        Preconditions.checkArgument(Event.belongsToSameAggregate(events));
+        AggregateId aggregateId = events.head().getAggregateId();
+        EntityManager entityManager = entityManagerFactory.createEntityManager();
+        final EntityTransaction transaction = entityManager.getTransaction();


We can handle this with TransactionRunner I believe

return Mono.fromRunnable(() -> TransactionRunner.runAndHandleException(entityManager -> { events.foreach(Throwing.runnable(e -> { JPAEvent jpaEvent = new JPAEvent(aggregateId, e.eventId(), jsonEventSerializer.serialize(e)); entityManager.persist(jpaEvent); })); }, e -> { throw new EventStoreFailedException("Unable to add events", e); });

Note that:

e variable name is ambiguous, we shall favor event

Wrap the whole transformation into a mono not just the final transformation

The TransactionWorker api isn't as shown above, but was easy enough to adjust. However the Throwing part I gave a few tries with several variations and types but couldn't get to work yet. If you have a working snippet that could save me some time trying to mess with the java/scala type system incompatibilities (Function1 is not a Function etc)...

btw I think it would have been nice if at least the events source api part remained in java (even if other module implementations were in scala) rather than making the interface itself use scala objects and have the scala types leak into the java code... scala was designed to try an play nice with java, but not necessarily the other way around. but perhaps that's just my own preference or lack of experience stitching them together :-)

For now I got it to work with JavaConverters.asJava(events), a bit ugly but I don't know how to get the scala objects to play nice with Throwing. If you have a better way let me know.

chibenwa · 2024-10-15T12:24:44Z

...ent-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/JPAEventStore.java

+            List<Event> events = (List<Event>) entityManager.createNamedQuery(SELECT_AGGREGATE_QUERY)
+                .setParameter("aggregateId", aggregateId.asAggregateKey())
+                .getResultStream()
+                .map(e -> {


Use THrowing.function ?

chibenwa · 2024-10-15T12:25:56Z

...ent-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/JPAEventStore.java

+    @Override
+    public Publisher<Void> remove(AggregateId aggregateId) {
+        EntityManager entityManager = entityManagerFactory.createEntityManager();
+        final EntityTransaction transaction = entityManager.getTransaction();


Use transaction runner here too and wrap the whole operation onto a mono...

chibenwa · 2024-10-15T12:26:21Z

...ent-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/JPAEventStore.java

+        return Mono.empty();
+    }
+
+    // for use in tests


Use @VisibleForTesting annotation them

chibenwa · 2024-10-15T12:26:55Z

...nt-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/model/JPAEvent.java

+        @Override
+        public int hashCode() {
+            return Objects.hashCode(aggregateId, eventId);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (this == obj) {
+                return true;
+            }
+            if (obj == null || getClass() != obj.getClass()) {
+                return false;
+            }
+            final JPAEventId other = (JPAEventId) obj;
+            return Objects.equal(this.aggregateId, other.aggregateId)
+                && Objects.equal(this.eventId, other.eventId);
+        }


We shall test equals and hash code with equals verifier.

Not sure what you mean here.

Not sure what you mean here.

Hello, you could use https://jqno.nl/equalsverifier/ for test

chibenwa · 2024-10-15T12:28:56Z

...nt-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/model/JPAEvent.java

+    @Column(name = "EVENT_ID", nullable = false)
+    private int eventId;
+
+    @Column(name = "EVENT", nullable = false, length = 16 * 1024)


This may hurt: are we sure this is enough to fit all possible serialized events?

For instance RuleSetDefined may be larger than this for people holding many filters...

Other implementation are unbounded on the size of this field, likely so should do the JPA one.

I suggest looking into using an unbounded byte[] here if need be..

I have no idea what this is used for and how big the events are, usually events and jsons (used in the other modules as well) are small-ish creatures :-)

I did start with 1mb and it errored, so just picked an arbitrary value to get through the prototype. I suppose if it needs to be a blob or whatnot we can do that. Maybe add to the contract (test) whatever size you think the implementations must support to make sure they're all compatible with the requirements?

changed to large @lob

chibenwa

Overall ok to me!

chibenwa · 2024-10-16T13:32:34Z

...ent-store-jpa/src/main/java/org/apache/james/eventsourcing/eventstore/jpa/JPAEventStore.java

+    @Inject
+    public void setJsonEventSerializer(JsonEventSerializer jsonEventSerializer) {


Can't we inject via the constructor?

ok, I moved both injections to a constructor, though other classes are inconsistent in constructor/setter injection point and I'm not sure if it matters... if you have a preference perhaps you should standardize the injection location throughout the code.

amichair · 2024-10-17T11:39:44Z

Next steps would be to wire the event store into existing app and expose features relying on event sourcing onto the same applications.

I don't know how/where/what is needed to finish integrating this, or if you intend on doing that separately after merging this PR?

amichair · 2024-10-22T05:55:07Z

Anything else to be done here? (ci failure seems unrelated?)

amichair force-pushed the JAMES-2433 branch from a329adc to 16173cf Compare October 15, 2024 10:44

chibenwa marked this pull request as draft October 15, 2024 12:16

chibenwa reviewed Oct 15, 2024

View reviewed changes

amichair force-pushed the JAMES-2433 branch 2 times, most recently from 9234fdd to 3f8f587 Compare October 16, 2024 11:30

chibenwa approved these changes Oct 16, 2024

View reviewed changes

JAMES-2433 Implement EventStore for a JPA backend

f587fe8

amichair force-pushed the JAMES-2433 branch from 3f8f587 to f587fe8 Compare October 17, 2024 11:28

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JAMES-2433 Implement EventStore for a JPA backend #2452

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amichair commented Oct 22, 2024

		@Inject
		public void setJsonEventSerializer(JsonEventSerializer jsonEventSerializer) {

JAMES-2433 Implement EventStore for a JPA backend #2452

Are you sure you want to change the base?

JAMES-2433 Implement EventStore for a JPA backend #2452

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amichair commented Oct 17, 2024

amichair commented Oct 22, 2024