Not clear how to return multiple columns using SQL union()

[cowwoc]

I am attempting to execute a UNION of three separate SQL queries as follows:

  QQueues q = QQueues.queues;
  QQueueDoctors qd = QQueueDoctors.queueDoctors;
  QAppointments a = QAppointments.appointments;
  List<Object[]> rows = session.query().union(
   session.subQuery(q).where(q.id.eq(queueId.getId())).
   leftJoin(qd).on(qd.queueId.eq(q.id)).
   leftJoin(a).on(a.queueId.eq(q.id)).list(q.name, qd.doctorId, a.id),
   session.subQuery(q).where(q.id.eq(queueId.getId())).
   leftJoin(qd).on(qd.queueId.eq(q.id)).
   rightJoin(a).on(a.queueId.eq(q.id)).list(q.name, qd.doctorId, a.id),
   session.subQuery(q).where(q.id.eq(queueId.getId())).
   rightJoin(qd).on(qd.queueId.eq(q.id)).
   rightJoin(a).on(a.queueId.eq(q.id)).list(q.name, qd.doctorId, a.id)).
   list();

Unfortunately, this query always returns 0 columns because UnionBuilder.list() won't allow me to specify which columns should be returned.

1. AbstractSQLQuery.UnionBuilder.list() uses union[0].getMetadata().getProjection() to determine the number of columns to return. This returns 3 for me. But later on this method invokes iterateMultiple() and...
2. iterateMultiple() invokes getMetadata().getProjection() to find out how many columns should be returned. This returns 0 for me.

As a result I end I with a List containing one element of zero columns even though it should have 3 columns. This bug is related to https://bugs.launchpad.net/querydsl/+bug/754910

[Timo Westkämper (timo-westkamper)]

Fixed. The QueryMetadata instance of the first union child is now used.

[Timo Westkämper (timo-westkamper)]

Released in 2.2.0-beta4