Avoid attempting to lock other deleted resources (#1835)

* Avoid attempting to lock other deleted resources

* 'Fix' cyclomatic complexity warning

internal/eea/eea.go

@@ -76,6 +76,7 @@ func (e *EEA) AggregateMiddleware(h message.HandlerFunc) message.HandlerFunc {
 	}
 }
 
+// nolint:gocyclo // TODO: hacking in the TODO about foreign keys pushed this over the limit.
 func (e *EEA) aggregate(msg *message.Message) (*message.Message, error) {
 	ctx := msg.Context()
 	inf, err := engine.ParseEntityEvent(msg)
@@ -91,13 +92,29 @@ func (e *EEA) aggregate(msg *message.Message) (*message.Message, error) {
 		Str("repository_id", repoID.String())
 
 	// We need to check that the resources still exist before attempting to lock them.
-	// TODO: handle artifact_id and pull_request_id or refactor this to remove the foreign keys.
+	// TODO: consider whether we need foreign key checks on the locks.
 	if _, err := e.querier.GetRepositoryByID(ctx, repoID); err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
 			logger.Msg("Skipping event because repository no longer exists")
 			return nil, nil
 		}
 	}
+	if artifactID.Valid {
+		if _, err := e.querier.GetArtifactByID(ctx, artifactID.UUID); err != nil {
+			if errors.Is(err, sql.ErrNoRows) {
+				logger.Msg("Skipping event because artifact no longer exists")
+				return nil, nil
+			}
+		}
+	}
+	if pullRequestID.Valid {
+		if _, err := e.querier.GetPullRequestByID(ctx, pullRequestID.UUID); err != nil {
+			if errors.Is(err, sql.ErrNoRows) {
+				logger.Msg("Skipping event because pull request no longer exists")
+				return nil, nil
+			}
+		}
+	}
 
 	res, err := e.querier.LockIfThresholdNotExceeded(ctx, db.LockIfThresholdNotExceededParams{
 		Entity:        entities.EntityTypeToDB(inf.Type),