java - Selecting from Multiple Tables in Spring Data

Question

I need to write a select query fetching data from multiple tables in Spring Data Repository layer. I know we can use @Query to write custom queries, but that returns value from a single table only?

SELECT s.service_id, s.name, us.rating_id 
FROM services s, 
     ratings r, 
     user_services us
where 
    us.service_id = s.service_id and
    us.rating_id = r.rating_id and
    us.user_id= ?;

Answer 1

Your Interface method can use native SQL to select columns from multiple tables and the method will return a list of object arrays :

public interface MyRepository extends JpaRepository {
  @Query(name = [name], nativeQuery = true)
  List<Object[]> methodThatQueriesMultipleTables();
}

Each item in the list is Object array that is a row of data

You can also create a Custom Repository Implementation :

How to add custom method to Spring Data JPA

@NoRepositoryBean
public interface CustomRepository<[Your object]> {
    List<Object[]> methodThatQueriesMultipleTables();
}

public class MyRepositoryImpl<[Your object]> implements CustomRepository<[Your object] {
    @PersistenceContext
    private EntityManager entityManager;

    @Override
    public List<Object[]> methodThatQueriesMultipleTables() {
        //use JPA query to select columns from different tables
        Query nativeQuery = entityManager.createNativeQuery("query");
        return query.getResultList();
    }
}