JPA CriteriaQuery multiselect from several entities - jpa

Question

Right now, I am using the method multiselect of CriteriaQuery to put some values from entity Termine in entity Task like this:
CriteriaBuilder builder = getEm().getCriteriaBuilder();
CriteriaQuery<Task> taskCriteria = builder.createQuery(Task.class);
Root<Termin> terminRoot = taskCriteria.from(Termin.class);
taskCriteria.multiselect(terminRoot.get("text"), terminRoot.get("empfaenger"), terminRoot.get("datVon"));
taskCriteria.where(builder.equal(terminRoot.get("empfaenger"), "000"));
List<Task> task = getEm().createQuery(taskCriteria).getResultList();
return task;
This is working fine, but now I am willing to gather the values text, empfaenger and datVon not only from the entity Termine but also from the entity Aufgabe, so that I will have a list of Tasks, that contains every Termin and Aufgabe which are having the same empfaenger.
Is it possible? If yes, how?
Thanks a lot in advance for your help!

Answer 1

I would derive both classes from task.
#Entity(name="Task")
#Inheritance(strategy = InheritanceType.JOINED)
#NamedQuery(name="Task.findAll", query="SELECT t FROM Task t")
public class Task {
#Id
Long id;
String text;
String empfaenger;
}
#Entity
public class Termin extends Task{
...
}
#Entity
public class Aufgabe extends Task{
...
}
And select them with a named query
List<Task> resultList = entityManager.createNamedQuery("Task.findAll",Task.class).getResultList();
or a criteria query with Task as Root.

Answer 2

This is the way I did to collect data from multiple entities (custom Select).
For example, multiple entities:
Root<InflowEntity> rootInflow = criteriaQuery.from(InflowEntity.class);
Root<OutflowEntity> rootOutflow = criteriaQuery.from(OutflowEntity.class);
You select the attributes you need from the above 2:
criteriaQuery.multiselect(rootInflow.get("inflowID"), rootInflow.get("name"),
rootOutflow.get("count"), rootOutflow.get("dateRange"));
Add the predicates (constraints) you need, for example:
Predicate[] predicates = new Predicate[2];
predicates[0] = criteriaBuilder.equal(rootInflow.get("uuid"), loginContext.getUuid());
predicates[1] = criteriaBuilder.equal(rootOutflow.get("uuid"), loginContext.getUuid());
Process the results:
criteriaQuery.where(predicates);
List<ResultsBean> results = session.createQuery(criteriaQuery).getResultList();
This Java bean (this is not the Hibernate entity), ResultsBean, stores the results. That is, it needs to have a constructor to accommodate the input the way the multiselect is arranged.