Spring Data JPA Query By Example with related entities

Question

I seem to be unable to add QueryByExample probes that match related entities.

@Entity
@Data
public class ArtistEntity implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String description;
    @ManyToMany(fetch = FetchType.EAGER)
    private Set<GenreEntity> genreList = new HashSet<>();
    @Version
    private Long version;
}

---

@Entity
@Data
public class GenreEntity implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @Version
    private Long version;
}

---

@Repository
public interface ArtistRepository extends JpaRepository<ArtistEntity, Long> {
}

When I try the following query, according to Hibernate's logs, my probe isn't running any conditions against the Genre

GenreEntity genreEntity = new GenreEntity();
genreEntity.setName("Heavy Metal");

ArtistEntity artistEntity = new ArtistEntity();

Set<GenreEntity> genreEntitySet = new HashSet<>();
genreEntitySet.add(genreEntity);

artistEntity.setGenreList(genreEntitySet);

Example<ArtistEntity> example = Example.of(artistEntity);
Pageable pagination = PageRequest.of(0, 10);
artistRepository.findAll(example, pagination);

---

I also tried looking on the Spring Data JPA documentation regarding QBE, but I didn't find anything specifically mentioning this limitation, which brought me to assume it's an unexpected behaviour.

Answer 1

Currently, you cannot do this with Query By Example.

The spring document states that this only works with SingularAttribute.

Currently, only SingularAttribute properties can be used for property matching. https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#query-by-example.running

You want to search by a property that is a Set<GenreEntity> (genreList), which is a PluralAttribute. It is not possible to search by this field.

It will be ignored when building a query, as can be seen here: https://github.com/spring-projects/spring-data-jpa/blob/master/src/main/java/org/springframework/data/jpa/convert/QueryByExamplePredicateBuilder.java#L127

You can use Specification.

Advanced Spring Data JPA - Specifications and Querydsl. https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/

For this you need to extend from interface JpaSpecificationExecutor:

public interface ArtistRepository extends 
    JpaRepository<ArtistEntity>, JpaSpecificationExecutor<ArtistEntity> {}

• And you also need to implement your custom Specification<T>.
• And then you can use findAll(Specification<T> spec, Pageable pageable).