JPA：反向映射字段上的查询子句-未设置参数

Question

I have make this simple domain in order to understand why the following query won't work.

@Entity
public class Owner {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToOne(cascade = CascadeType.ALL)
    private Reverse reverse;

    //getters / setters
}

@Entity
public class Reverse {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToOne(mappedBy = "reverse")
    private Owner owner;

    //getters / setters
}

This test fails:

@Test
@Transactional
public void testQueryByEntity() throws Exception {
    Reverse reverse = new Reverse();
    Owner owner = new Owner();

    owner.setReverse(reverse);
    entityManager.persist(owner);

    entityManager.flush();
    entityManager.clear();

    Reverse dbReverse =
            em.createQuery("from Reverse r where r.owner = :owner", Reverse.class)
                    .setParameter("owner", owner)
                    .getSingleResult();

    System.out.println("Revrse id: " + dbReverse.getId());
}

with the following exception:

Caused by: org.h2.jdbc.JdbcSQLException: Parameter "#2" is not set; SQL statement:
select reverse0_.id as id1_ from T_ORDER reverse0_ where reverse0_.id=? limit ? [90012-156]

Same query from Owner side works:

Owner dbOwner = 
    em.createQuery("from Owner o where o.reverse = :reverse", Owner.class)
        .setParameter("reverse", reverse)
        .getSingleResult();

In order to make the query work I need to modify it in this way:

Reverse dbReverse = 
    em.createQuery("from Reverse r where r.owner.id = :ownerId", Reverse.class)
        .setParameter("ownerId", owner.getId())
        .getSingleResult();

So my question is:

why if in where clause I have this reverse mapping condition, I need to query r.owner.id and not simply r.owner in order to make my query works?

Thank you!

Answer 1

since Owner class is the actual owner of the relationship and hence reverse table's primary key is available inside Owner table as a foreign key.

so if you refer reverse from owner table(owner.reverse) you can get it using the mapping reverse id which is available inside Owner table.

but the reverse mapping is - reverse table will not have Owner table's id in its table and hence if you try to say reverse.owner it cant fetch it from its table.

so you have to use reverse.owner.id to get the id from opposite table.