Spring JPA repository and QueryDsl how to force left join - spring-data-jpa

Question

Let's say I have two entities User and Task, each user can have one task.
The issue that I'm facing is if I have one record in the user table whose email starts with a and there are no records at all in the task table.
This snippet below will return no records although I would expect users that have mail starting with a.
UserRepository in example extends QuerydslPredicateExecutor.
userRepository.findAll(
QUser.user.email.startsWith("a")
.or(QUser.user.task.text.contains("something"))
)
If I check logs, Hibernate is creating cross join with user.task_id=task.id as a part of where clauses. This type of join automatically discards users whose mails are starting with a if they don't have a task assigned.
Is there a way to force usage of left join instead of a cross join in findAll method of the repository?
I know I can do it by using JPAQuery but then I would have to reimplement paging functionality...
JPAQuery query = new JPAQuery(entityManager);
query
.from(QUser.user)
.leftJoin(QTask.task)
// ...

Answer 1

I am not sure if we can do that since the findAll implementation is generated for us. However we can pass a predicate in the findAll method which will help deal with issue you are encountering.
You can try to do something like this:
QUser qUser = QUser.user;
QTask qTask = QTask.task;
JPQL<UserEntity> userJpqlQuery = JPAExpressions.selectFrom(qUser)
.leftjoin(qUser.task, qTask)
.where(qUser.email...., qTask.text...);
userRepository.findAll(qUser.in(userJpqlQuery));
In the code above I have used Querydsl, which is an alternative to CriteriaBuilder and is type safe. Then I have created a subquery to make the selection I want and return the all users matching the subquery.
In the end , hibernate should generate something like this:
select * from User qUser0 where qUser0.id.in(
select qUser1.id from User qUser1
left join Task qTask0 on
qUser1.taskId = qTask0.id
where ...
);