如何使用JPA map native query into nested projection

Question

I have two tables, User and Roles, they are many-to-many

Also they are large tables, don't expect all irrelevant column returns.

So I have native query, (and have to use native).

select u.name, r.name, r.uuid
from user u
       join user_role_join urj on urj.user_uuid = u.uuid
       join role r on r.uuid = urj.role_uuid;

From return, one user show multiple roles.

Adam | superAdmin | {uuid1}
Adam | admin      | {uuid2}
Lisa | guest      | {uuid3}
...

I need make returns to fit with pojo

User
 String name,
 List<Role> roles;

Role
 String name,
 UUID uuid

I'm using EntityManager to do the query.

How could I make JPA know map one user with multiple Roles?

{
 name:Adam
 roles:[
 {
   uuid:{uuid1}
   name:superAdmin
 },
 {
   uuid:{uuid2}
   name:admin
 }
 ]
},
{
 name:Lisa
 roles:[
 {
   uuid:{uuid3}
   name:guest
 }
 ]
} 

Answer 1

I don't know why you need to use a native query, but when collections are involved, JPA/Hibernate can only help you when using entities.

If you want avoid unnecessary select items, I can recommend you try to use a JPA model with Blaze-Persistence as this is a perfect use case forBlaze-Persistence Entity Views .

I created the library to allow easy mapping between JPA models and custom interface or abstract class defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure(domain model) the way you like and map attributes(getters) via JPQL expressions to the entity model.

A DTO model for your use case could look like the following with Blaze-Persistence Entity-Views:

@EntityView(User.class)
public interface UserDto {
    @IdMapping
    UUID getId();
    String getName();
    Set<RoleDto> getRoles();

    @EntityView(Role.class)
    interface RoleDto {
        @IdMapping
        UUID getUuid();
        String getName();
    }
}

Querying is a matter of applying the entity view to a query, the simplest being just a query by id.

UserDto a = entityViewManager.find(entityManager, UserDto.class, id);

The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features