JPQL Select Entity and Get count on collection that belongs to selected entity

Question

I've got an entity A with a collection of B elements.

I would like to create a query that basically does this:

Select a, count(b) from A a  inner join fetch a.b b group by a

I was hoping to get an Array Object where element 0 is my A entity and element 1 is a Number which is the number in the collection.

Jpa (backed by hibernate) throws the following error:

Caused by: java.sql.SQLException: Not in aggregate function or group by clause:   org.hsqldb.Expression@16d829b1 in statement (sql query)

When i copy and paste the native sql from the error into postgres, it doesn't work.

When i copy and paste the native sql from the following JPQL query:

Select a, count(b) from A a  inner join fetch a.b b group by a, b

Postgres returns the expected results. The problem is Hibernate still coughs up the same error as the first Query.

Answer 1

试试这个：

SELECT DISTINCT a, a.b.size FROM A a INNER JOIN FETCH a.b b