Create spring repository without entity

1. Custom Repository with @Repository Annotation:

@Repository
public class CustomNativeRepositoryImpl implements CustomNativeRepository {

    @Autowired
    private EntityManager entityManager;

    @Override
    public Object runNativeQuery() {
        entityManager.createNativeQuery("myNativeQuery")
         .getSingleResult();
    }
}

2. Implementing JpaRepository with Query:

public interface ProductFilterRepository {
    Page<Product> filter(FilterTO filter, Pageable pageable);
}



@Repository
@AllArgsConstructor
public class ProductFilterRepositoryImpl implements ProductFilterRepository {

    private final EntityManager em;

    @Override
    public Page<Product> filter(FilterTO filter, Pageable pageable) {
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Product> cq = cb.createQuery(Product.class);
        Root<Product> root = cq.from(Product.class);
        List<Predicate> predicates = new ArrayList<>();

        if (filter.getPriceMin() != null) {
            predicates.add(cb.ge(root.get("price"), filter.getPriceMin()));
        }
        if (filter.getPriceMax() != null) {
            predicates.add(cb.le(root.get("price"), filter.getPriceMax()));
        }
        if (filter.getBrands() != null && !filter.getBrands().isEmpty()) {
            predicates.add(root.get("brand").in(filter.getBrands()));
        }
        if (filter.getCategories() != null && !filter.getCategories().isEmpty()) {
            predicates.add(root.get("category").in(filter.getCategories()));
        }
        cq.where(predicates.toArray(new Predicate[0]));
        TypedQuery<Product> tq = em.createQuery(cq);
        tq.setMaxResults(pageable.getPageSize());
        tq.setFirstResult(pageable.getPageNumber() * pageable.getPageSize());

        CriteriaQuery<Long> countCq = cb.createQuery(Long.class);
        countCq.select(cb.count(countCq.from(Product.class)));
        countCq.where(predicates.toArray(new Predicate[0]));
        TypedQuery<Long> countTq = em.createQuery(countCq);
        Long count = countTq.getSingleResult();

        return new PageImpl<>(tq.getResultList(), pageable, count);
    }
}

3. Create a Dummy Entity and Use JpaRepository:

@Entity
public class RootEntity {
    @Id
    private Integer id;
}

@Repository
public interface MyRepository extends JpaRepository<RootEntity, Integer> {
}

4. Using JdbcTemplate:

@Repository
public class MyRepository {

    @PersistenceContext
    EntityManager entityManager;

    public void doSomeQuery(){
        Query query = entityManager.createNativeQuery("SELECT foo FROM bar");
        query.getResultsList()
        ...
    }

}

5. Create Custom Interface and Use @Query:

@Repository
public class CustomNativeRepositoryImpl implements CustomNativeRepository {

    @PersistenceContext
    EntityManager entityManager;

    @Override
    public Object runNativeQuery() {
        Query query = entityManager.createNativeQuery("myNativeQuery")
         .getSingleResult();
    }
}