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<PersonAttribute> attributes;
}

@Entity
PersonAttribute {
    @ManyToOne
    AttributeName attributeName;

    String attributeValue;
}

@Entity
AttributeName {
    String name;
}

I have a Spring-Data-JPA repository defined such as:

public interface PersonRepository extends PagingAndSortingRepository<Person, Long>, QueryDslPredicateExecutor<Person>{}

I see in the QueryDSL documentation that there is a mechanism to Join from the Person to the PersonAttribute, but it looks like you need access to the QueryDsl Query object, which the client of the repository wouldn't have.

What I would like to do with my Predicate is to find all those Persons that have an AttributeValue (there's one join) with a value of "blue" and an AttributeName (there's another join) with a name of "eyecolor". I'm not sure how I would do that with an any() and enforce that I only get those with eye_color=blue and not those with shoe_color=blue.

I was hoping I could do something like this:

QPerson person = QPerson.person;
QPersonAttribute attribute = person.attributes.any();

Predicate predicate = person.name.toLowerCase().startsWith("jo")
    .and(attribute.attributeName().name.toLowerCase().eq("eye color")
          .and(attribute.attributeValue.toLowerCase().eq("blue")));

but with the any() in there it just matches anything with an attribute value of "blue" and anything with an "eye color" attribute regardless of color. How I can make those conditions apply to the same attribute within the set?

Answer 1

You can't directly join a column in a predicate but you can create an any() expressions like this

QPerson.person.attributes.any().attributeValue.eq("X")

This approach has the restriction that the join expression QPerson.person.attributes.any() can be used in only one filter. It has though the benefit that this expression is internally converted into a subquery which doesn't conflict with paging.

For multiple restrictions you will need to construct a subquery expression explicitly like this

QPersonAttribute attribute = QPersonAttribute.personAttribute;
new JPASubQuery().from(attribute)
    .where(attribute.in(person.attributes),
           attribute.attributeName().name.toLowerCase().eq("eye color"),
           attribute.attributeValue.toLowerCase().eq("blue"))
     .exists()

In addition to QueryDslPredicateExecutor you can also use Querydsl queries via Spring Data like this

public class CustomerRepositoryImpl
 extends QuerydslRepositorySupport
 implements CustomerRepositoryCustom {

    public Iterable<Customer> findAllLongtermCustomersWithBirthday() {
        QCustomer customer = QCustomer.customer;
        return from(customer)
           .where(hasBirthday().and(isLongTermCustomer()))
           .list(customer);
    }
}

Example taken from here https://blog.42.nl/articles/spring-data-jpa-with-querydsl-repositories-made-easy/

Answer 2

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<T> {

    Page<T> findAll(JPQLQuery<T> jpqlQuery, Pageable pageable);

}

Implementation:

@Repository
public class QueryDslRepositoryImpl<T> implements QueryDslRepository<T> {

    @PersistenceContext
    private EntityManager entityManager;

    @Override
    @SuppressWarnings("unchecked")
    public Page<T> 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<T> 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<Customer, Long>, QueryDslRepository<Customer>,
        QuerydslPredicateExecutor<Customer> {

}

Actual repository invocation:

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

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

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