Create spring repository without entity

问题

I want to use spring data repository interface to execute native queries - I think this way is the simplest because of low complexity.

But when extending interface ex. CrudRepository<T, ID> I need to write T - my entity, which is not available.

My native queries does not return any concrete entity, so what is the best way to create spring repository without entity?

回答1:

CrudRepository or JpaRepository were not designed to work without an <Entity,ID> pair.

You are better off creating a custom repo, inject EntityManager and query from there:

  @Repository
  public class CustomNativeRepositoryImpl implements CustomNativeRepository {

    @Autowired
    private EntityManager entityManager;

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

回答2:

Currently there is no functionality in JPA to create repositories with only native or even JPQL queries (using @Query notation). To get around this, you can create a dummy object to insert into the extension interface like below:

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

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

回答3:

You can just annotate your implementation with @Repository, and get an instance of EntityManager.

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);
    }
}

回答4:

I think that using JdbcTemplate can be considered as an alternative when you do not have a concrete entity class for the resultset of a native query. Querying data using JdbcTemplate requires a POJO class for the resultset and a mapper implementing the RowMapper interface for the POJO class.

回答5:

If you are using JPA you need Entities. As previous answers you can create NativeQueries or use Criteria API directly from EntityManager.

Some documentation about custom reports and common repo behaviour:

https://docs.spring.io/spring-data/data-commons/docs/1.6.1.RELEASE/reference/html/repositories.html#repositories.custom-behaviour-for-all-repositories

来源：https://stackoverflow.com/questions/55513776/create-spring-repository-without-entity