JPQL Entity1 join Entity2 where Entity1 is mapped in Entity2 but not the other way round

Question

If I have two Entities Entity1 and Entity2 which are mapped on both sides (or at least Entity2 is mapped in Entity1) I can do

select e1 from Entity1 e1
left join e1.entity2 e2
where e2.id is null

Is there an equivalent for this if I do not have e1.entity2 but only Entity2.entity1 ?

Answer 1

I'd personally change your tables round the other way. There is an option of using RIGHT JOIN but I would fail any code if I saw a RIGHT JOIN during a code review;

SELECT *
FROM Entity2 e2
LEFT JOIN Entity1 e1
    ON e2.IdField = e1.IdField
WHERE e1.IdField IS NULL

Also, you appear to be missing your join criteria, it's best to declare these