I get the following exception when using the getEvents method:
org.hibernate.MappingException: Unknown entity: java.lang.Long
public List<Long> getEvents(Person person) {
String q = "select new java.lang.Long(te.event_id) "
+ "from teachers_event te"
+ "where te.teachers_id = :personId ";
Query query = entityManager.createNativeQuery(q, Long.class);
query.setParameter("personId", person.getId());
return (List<Long>) query.getResultList();
}
The teachers_event table in database connects the id of teacher with the event. I don't map this table to an entity. I only want to get the ids from it. The ids in the PostgreSQL table are bigint. Is there any way to achieve it without making a separate class to map the TeacherEvents entity?
In JPA 2.1 there is a feature called "result set mapping".
Basically you have to define a POJO class which would hold the result values (all the values must be passed using the constructor):
public class IdResult{
private Object id;
public IdResult(Object id){
this.id = id;
}
public Long getLongId(){
return (Long)id;
}
}
Then you have to declare the mapping on one of your entities (does not matter on which, it just has to be a declated @Entity):
@SqlResultSetMapping(name="IdMapping", classes = {
@ConstructorResult(targetClass = IdResult.class,
columns = {@ColumnResult(name="id")})
})
You would have to use an alias in your query to match the @ColumnResult name:
select te.event_id as id
...
And finally use in the query creation:
Query query = entityManager.createNativeQuery(q, IdMapping.class);
return (List<IdResult>) query.getResultList();
Then in your service layer you would just use getLongId();
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