JPA 2 No explicit selection and an implicit one cold not be determined

Question

I am trying to fetch all users for a folder where the user was created after a certain date. the relationship between the user and the folder lives in a seperate table.

Answer 1

I had the exact same error today. The funny thing is that I grabbed my example from Hibernate 3.6.3.Final docs. Their example is:

CriteriaQuery query = builder.createQuery();
Root men = query.from( Person.class );
Root women = query.from( Person.class );
Predicate menRestriction = builder.and(
    builder.equal( men.get( Person_.gender ), Gender.MALE ),
    builder.equal( men.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE )
);
Predicate womenRestriction = builder.and(
    builder.equal( women.get( Person_.gender ), Gender.FEMALE ),
    builder.equal( women.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE )
);
query.where( builder.and( menRestriction, womenRestriction ) );

What I did to "fix" the error is explicitly select the root. Note I had to create one root to solve this. Here is my example:

CriteriaQuery query = builder.createQuery();
Root personRoot = query.from( Person.class );
Predicate menRestriction = builder.and(
    builder.equal( personRoot.get( Person_.gender ), Gender.MALE ),
    builder.equal( personRoot.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE )
);
Predicate womenRestriction = builder.and(
    builder.equal( personRoot.get( Person_.gender ), Gender.FEMALE ),
    builder.equal( personRoot.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE )
);
query.select(personRoot);
query.where( builder.and( menRestriction, womenRestriction ) );

What I can't figure out is why an implicit selection could not be made. In Hibernate's example the only class that is used is Person.class. I'll update my response when I dig in a little further.