JPA Join over multiple Entities

Question

My Problem is as follows

@Entity
public class MainType{
    @Fetch(FetchMode.JOIN)
    @ManyToOne(fetch = FetchType.EAGER)
    private SubType subObject;
}

@Entity
public class SubType{
    @Fetch(FetchMode.JOIN)
    @ManyToOne(fetch = FetchType.EAGER)
    private SubSubType subsubObject;
}

When I query the MainType with Hibernate to recieve a Collection hibernate will make a join. Something like select * from MainType left join SubType which is good but then it makes another select for each record that the first query returned to load SubSubType. I would like to load everything in a single query like select * from MainType left join SubType left join SubSubType.

Do you know any way to make that happen?

Does [this question](http://stackoverflow.com/questions/32453989/what-is-the-solution-for-the-n1-issue-in-hibernate) help you? Otherwise, could you post your code? — acm, Feb 10 '17 at 09:00

Naros · Answer 1 · 2017-02-09T14:16:00.037

0

In HQL/JPQL you'd write that almost as you mentioned:

SELECT mt FROM MainType mt 
  LEFT JOIN FETCH mt.subObject so 
  LEFT JOIN FETCH so.subSubObject sso

The key is to apply a JOIN FETCH and not just a JOIN to avoid the additional query that will fetch the objects after acquiring the identifiers.

edited Feb 09 '17 at 14:16

answered Feb 09 '17 at 14:09

Naros

19,928
3
41
71

Yes I thought about that way too. But i am Using the Criteria API for querying. And aditionally i want all the querys for MainType to look like this not only the one i am writing now. Isn't there a chance to force this way of querying inside the modeldeclaration. – Mr.H. Feb 10 '17 at 08:13

JPA Join over multiple Entities

1 Answers1