Join array in hibernate

Question

I have 2 entities: A and B.

@Entity
@Table(name = "A")
class A{
    @Id
    private long id;

    @OneToMany(mapped by="a")
    private Set<B> b;
}

@Entity
@Table(name = "B")
class B{
    @Id
    private long id;

    @ManyToOne
    @JoinColumn(name="a")
    private A a;
}

When i'm trying to make something like

Query q=sessionFactory.openSession().createQuery("select a.id, bArray
 from A as a join a.b as bArray");

i'm getting not collection of B, but one B-object. How can i get A-class and collection of related with it B-objects? I.e. in debugger there is not Set with 1 element, there is just B-element.

select distinct a from A a left join fetch a.b will return the As, each with its loaded set of Bs. There's no way to do what you want. — JB Nizet
– JB Nizet, Commented Aug 31, 2015 at 12:42

Community · Accepted Answer · 2017-05-23 12:14:35Z

2

Query q=sessionFactory.openSession().createQuery("select a.id, bArray
 from A as a join a.b as bArray");

With above query, you will get only one object for B not a collection because basically the query is just performing the join between A and B and returning all the possible tuples ( select a , b from A as a inner join B as b)

You can set a custom result transformer for custom results processing like this

But anyway in your case, you can simply pre-fetch "b" objects along with "a" object by using join fetch as below query.

Query q=sessionFactory.openSession().createQuery("select a from A as a join fetch a.b ");

edited May 23, 2017 at 12:14

CommunityBot

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answered Aug 31, 2015 at 12:51

Anudeep Gade

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