I'm learning Hibernate and I'm wondering what's the use of the JOIN clause within a HQL query. I might be wrong, but it seems to me that you can always do without.
Let's say I have a ChildClass entity which has a mapped @ManyToOne relationship with a ParentClass.
Now I can build a HQL query like this:
session.createQuery("FROM ChildClass ch WHERE ch.parentClass.id=1L")
As you can see I could filter the results by the parent class' id field, accessing it through the child class: ch.parentClass.id
If I wanted to do the same in SQL, I'd need to perform a JOIN, and the query would be the following:
SELECT * FROM ChildTable ch
JOIN ParentTable p ON (ch.parent_id = p.id)
WHERE p.id=1;
If I got this straight, in HQL I don't need to include any JOIN in my query, because the @ManyToOne mapped relationship implicitly joins the two entities. So why would I ever use JOIN in a HQL query? Is there any specific kind of situations where JOIN is necessary?
There are several situations where explicitly specifying the join is useful
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