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

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 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/