左联接获取可为空的孙子关联会导致NPE处于休眠状态

Question

I have an entity called Foo. It has a nullable many-to-one association to Bar. Bar has a non-nullable many-to-one association to Baz.

My goal is to grab all Foo entities and eagerly fetch their Bar associations and, for those foo where foo.bar is non-null, eagerly fetch foo.bar.baz.

Is this possible? The following both cause hibernate to throw a NullPointerException inside its query engine:

select f from Foo f left join fetch f.bar left join fetch f.bar.baz

select f from Foo f left join fetch f.bar.baz

Now, this works:

select f from Foo left join fetch f.bar

But that doesn't eagerly fetch f.bar.baz for those f with non-null bar.

Answer 1

You need to alias bar in your query:

select f from Foo f
  left join fetch f.bar b
  left join fetch b.baz