[SOLVED] Hibernate CriteriaAPI Fetch only very specific attribute of many to one related entity

Hibernate CriteriaAPI Fetch only very specific attribute of many to one related entity

I have 2 classes similar to this:

public class A {
    @Id @GeneratedValue
    private long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "b_id")
    B b;

    ...
}

public class B {
    @Id @GeneratedValue
    private long id;

    ...
}

I want to make a query using the Criteria API that queries the A table, but for future queries, having the id of the b many to one relationship is important.

So far I've found I can use

var root = query.from(A.class);
root.fetch(A_.b);
...

When I look at the underlying SQL this produces, this will cause all basic attributes of B to be fetched.

What I'm looking for is to (without falling back on HQL) do something like

var root = query.from(A.class);
root.join(A_.b).fetchBasicAttribute(B_.id);
...

Resulting in instances of A linking to instances of B where only the id is populated. (Ideally I'd also like to be able to specify other attributes of B too)

Is something like this possible?

Solution

That's not really possible with Hibernate right now. Note though that the primary key i.e. id attribute is the one that the foreign key column refers to, so you don't have to fetch that attribute, it will be populated in the proxy object that is created automatically.