Support search result classes different from Specification query root [DATAJPA-51] about spring-data-jpa HOT 3 OPEN

Kamil commented

For our project is important to use Specification together with DTO created in JPQL.

Is there any possibility it will be supported? I see that this issue have a lot of votes...

from spring-data-jpa.

we need this

from spring-data-jpa.

in Hexagonal Architecture for example we have a domain class and a jpaEntity class;

• the domain class could be:

class User {
   private String id;
   private String fullname;
   private String phone;
   private String stuff;
   ...
}

and

class Wallet {
   private String id;
   private String balance;
   private User user; // we could have a constructor (lite modal) with only fullname / id
   ...
}

• the corresponding jpa entities could be:

class UserJpaEntity {
   private String id;
   private String fullname;
   private String phone;
   private String stuff;
   ...
}

and

class WalletJpaEntity {
   private String id;
   private String balance;
   private String userId;
   ...
}

now due to Hexagonal Architecture, we can't just use @ OneToOne or such annotations to link jpa entities and call it a day, I think..

Let's tackle the problem;

To fetch List/Page of Wallets for example, with their Users, one might fetch all wallets then loop through them and fetch the User, and that sounds like n+1 problem 🤔

or we can simply make a custom Wallet constructor and use it to map the result with @ Query, like the following:

@Query("""
        SELECT new io.spring.demo.Wallet(w.id, w.balance, u.id, u.fullname) FROM WalletJpaEntity w
        INNER JOIN UserJpaEntity u ON u.id = w.userId
        """)
Page<Wallet> findWallets(Pageable pageable);

and this works 🎉

But...

For filtering for example, we would need to use Specification API (that's why I'm commenting on this Issue), like this:

@Query("""
        SELECT new io.spring.demo.Wallet(w.id, w.balanace, u.id, u.fullname) FROM WalletJpaEntity w
        INNER JOIN UserJpaEntity u ON u.id = w.userId
        """)
Page<Wallet> findWallets(Specification<WalletJpaEntity> spec, Pageable pageable);

which doesn't work currently....

any work around this to assure we can have dynamic filters + efficient queries with joins (custom result mapping) at the same time ?

PS: A StackOverFlow question with same issue

from spring-data-jpa.