I have 3 entities and nested collections of them as follows:
Entity A contains collection of B
Entity B contains collection of C

And I need to fetch a list of full object graphs of entity A. When I set fetching strategy to "subselect" both for collection of B and collection of C, actually only collection of B is read via single query. Each collection of C is read via separate query per each entity of type B - the same as if fetching strategy was "select" there.

So I expect the following:
select ... from A
select ... from B where a_id in (select id from A)
select ... from C where b_id in (select id from B where a_id in (select id from A))

But actually get:
select ... from A
select ... from B where a_id in (select id from A)
select ... from C where b_id = ?
select ... from C where b_id = ?
...
select ... from C where b_id = ?

Are there any limitations on nested subselects?