QueryDSL fetchJoin does not fetch the data

Question

I am facing this issue:

Lets assume I have 3 entities like this:

Entity A:

long id

String someField

// No bidirectional linkage to B entity via hibernate

Entity B:

long id

String someBField

@ManyToOne(optional = false, fetch = FetchType.LAZY)
@JoinColumn(name="b_id")
A entityA

@ManyToOne(optional = true, fetch = FetchType.LAZY)
@JoinColumn(name="b_id")
C entityC;   

Entity C:

long id

String someCField

// No bidirectional linkage to B entity via hibernate

Now, the goal is to (for simplicity, there are some ordering and filtering but that does not affect my question) return all B records, every one with A and C record fetched

So I am doing something like this (I am used to use spring-data-jpa to (LEFT) JOIN FETCH the properties to avoid lazy loading on demand to prevent firing useless queries into database and I want to do exactly same thing in QueryDSL)

    JPAQuery<DealBo> query = new JPAQuery<>(entityManager);

    query.select(qB)
            .from(qB)
            .innerJoin(qA).on(qA.a_id.eq(qB.id)).fetchJoin()
            .innerJoin(qC).on(qC.a_id.eq(qB.id)).fetchJoin()
            .fetch()

And I expect one SQL where in select clause there are data from all 3 tables (entities), where QueryDSL (or Hibernate, I am not completely sure what tool will do SQL -> Entity mapping) map the result to Entity objects. But what I am really getting is just select like

select b.id, b.someBfield from b
inner join a // join clause is right and omitted for simplicity
inner join b // join clause is right and omitted for simplicity

So when I call on one item what QueryDSL returned for example

b.getC() or b.getA(), I am firing another queries into database, what is a thing I want to avoid in first place.

What am I doing wrong?

Answer 1

I think, the definitions of the join conditions are inappropriate.

Hopefully I have recreated the described constellation with UserEntity <- UserRoleEntity -> RoleEntity:

@Entity
@Table(name = "t_user")
public class UserEntity {

    @Id
    @Column(name = "id")
    private Integer id;
    @Column(name = "name") 

    // ..
}

@Entity
@Table(name = "t_user_role")
public class UserRoleEntity {
    @Id
    @Column(name = "id")
    private Integer id;
    @ManyToOne
    @JoinColumn(name = "user_id")
    private UserEntity user;
    @ManyToOne
    @JoinColumn(name = "role_id")
    private RoleEntity role;

    // ..
}

@Entity
@Table(name = "t_role")
public class RoleEntity {
    @Id
    @Column(name = "id")
    private Integer id;
    @Column(name = "name")
    private String name;

    // ..
}

The query

List<UserRoleEntity> findAll() {
    JPAQuery<UserRoleEntity> query = new JPAQuery<>(entityManager);

    return query.select(QUserRoleEntity.userRoleEntity)
            .from(QUserRoleEntity.userRoleEntity)
            .innerJoin(QUserRoleEntity.userRoleEntity.user).fetchJoin()
            .innerJoin(QUserRoleEntity.userRoleEntity.role).fetchJoin()
            .fetch();

}

fetches the associated tables and a subsequent iteration over the user-association does not load the user entity from database.

The generated SQL looks like

    select 
        userroleen0_.id as id1_5_0_, 
        userentity1_.id as id1_4_1_, 
        roleentity2_.id as id1_2_2_, 
        userroleen0_.role_id as role_id2_5_0_, 
        userroleen0_.user_id as user_id3_5_0_, 
        userentity1_.name as name2_4_1_, 
        roleentity2_.name as name2_2_2_ 
    from t_user_role userroleen0_ 
    inner join t_user userentity1_ on userroleen0_.user_id=userentity1_.id 
    inner join t_role roleentity2_ on userroleen0_.role_id=roleentity2_.id