Question

我正在尝试从其他查询中选择信息，例如：

SELECT user.user_id, product.first_time
FROM USER AS user
INNER JOIN (SELECT min(product.first_time) as first_time,
                   product.user_id
            FROM PRODUCT AS product
            GROUP BY (product.user_id)
           ) product
ON user.user_id = product.user_id

但我不知道如何创建一个Criteria Query来执行它。我可以使用Criteria API执行它吗？

Answer 1

尝试使用此： https://docs.jboss.org/hibernate/orm/4.3/topical/html/metamodelgen/MetamodelGenerator.html

需要创建元类你的实体。

示例，您的服务类：

@Service("jpaCustomerService")
@Repository
@Transactional

public class CustomerServiceImpl implements CustomerService {
    @PersistenceContext
    private EntityManager em;

@Transactional(readOnly = true)
    public List<CustomersEntity> findByCriteriaQuery(String name){
        CriteriaBuilder cb = em.getCriteriaBuilder();
        javax.persistence.criteria.CriteriaQuery<CustomersEntity> criteriaQuery = cb.createQuery(CustomersEntity.class);
        Root<CustomersEntity> customersEntityRoot = criteriaQuery.from(CustomersEntity.class);
        customersEntityRoot.fetch(CustomersEntity_.animal, JoinType.LEFT);
        criteriaQuery.select(customersEntityRoot).distinct(true);
        Predicate criteria = cb.conjunction();
        if (!name.isEmpty()){
            Predicate p = cb.equal(customersEntityRoot.get(CustomersEntity_.name), name);
        criteria = cb.and(criteria, p);
        }
        criteriaQuery.where(criteria);
        List<CustomersEntity> result = em.createQuery(criteriaQuery).getResultList();
        return result;
    }
}

和你的控制者或你的主人：

public static void criteriaExample(GenericXmlApplicationContext ctx){
        CustomerService service = ctx.getBean("jpaCustomerService", CustomerService.class);
        List<CustomersEntity> creteriaResult = service.findByCriteriaQuery("NCI-3");
        for (CustomersEntity customer : creteriaResult){
            System.out.println(customer);
            if (!customer.getAnimal().isEmpty())
            for (AnimalsEntity animal : customer.getAnimal()){
                System.out.println(animal);
            }
        }
    }

CustomersEntity_ - 元模型类。不需要SQL查询。

你的infs是：

public interface CustomerService {
List<CustomersEntity> findByCriteriaQuery(String name);}

JPA Criteria从另一个查询中选择

1 个答案: