Spring-Data-JPA with QueryDslPredicateExecutor and Joining into a collection

Question

Let\'s say I have a data model like this (pseudocode):

@Entity
Person {
    @OneToMany
    List attributes;
}

@Entity
PersonAttribute {
          


        

Answer 1

In order to perform more complex queries I've created my custom QueryDslRepository with support of JPQL queries and spring data JPA pagination.

Interface:

public interface QueryDslRepository {

    Page findAll(JPQLQuery jpqlQuery, Pageable pageable);

}

Implementation:

@Repository
public class QueryDslRepositoryImpl implements QueryDslRepository {

    @PersistenceContext
    private EntityManager entityManager;

    @Override
    @SuppressWarnings("unchecked")
    public Page findAll(JPQLQuery jpqlQuery, Pageable pageable) {
        Assert.notNull(jpqlQuery, "JPQLQuery must not be null!");
        Assert.notNull(pageable, "Pageable must not be null!");

        Querydsl querydsl = new Querydsl(entityManager, new PathBuilderFactory()
                                         .create(jpqlQuery.getType()));

        JPQLQuery countQuery = ((AbstractJPAQuery) jpqlQuery).clone(entityManager);
        AbstractJPAQuery query = (AbstractJPAQuery) querydsl.applyPagination(pageable, jpqlQuery);
        return PageableExecutionUtils.getPage(
                  // Clone query in order to provide entity manager instance.
                  query.clone(entityManager).fetch(), 
                  pageable, 
                  countQuery::fetchCount);
    }

}

Example of use:

@Repository
public interface CustomerRepository extends JpaRepository, QueryDslRepository,
        QuerydslPredicateExecutor {

}

Actual repository invocation:

 BooleanBuilder predicates = new BooleanBuilder();
 predicates = predicates.and(QCustomer.customer.active.eq(true));

 JPQLQuery q = new JPAQuery()
            .select(QCustomer.customer)
            // You can use .join() method here.
            .where(predicates);

 Page result = customerRepository.findAll(q, Pageable.unpaged());