JPA2，没有实体映射的联接条件查询

Question

我有以下表格：

• 客户

• 订单

  @Entity
  public class Customer {
  String id;
  }
  @Entity
  public class Order {
  String id;
  String customerId;
  }
  

我没有用在它们之间建立实体的映射；然而，我需要一个查询，它应该连接这两个表：

final CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
final CriteriaQuery<Customer> criteriaQuery = criteriaBuilder.createQuery(Customer.class);
final Root<Customer> root = criteriaQuery.from(Customer.class);
final Join<Order, Customer> joinOrder = root.join(Order_.customerId.getName()); // doesn't work
final TypedQuery<Customer> queryData = entityManager.createQuery(
criteriaQuery
.where(
criteriaBuilder.lessThan(root.get(Customer_.creationDate), date)
// should add a predicate with order properties
)
);

return queryData.getResultList();

有没有可能用JPA2做类似上面的事情？

Answer 1

• 您可以使用子查询

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Customer> customerQuery = 
cb.createQuery(Customer.class);
Root<Customer> customerRoot = customerQuery.from(Customer.class);
Subquery<Order> subQuery = customerQuery.subquery(Order.class);
Root<Order> orderRoot = subQuery.from(Order.class);
//Replace this with the restriction you want to apply to order
Predicate predicate= orderRoot.get("xxxxx").in(xxx, xxx);
subQuery.select(orderRoot.get("customerId")).where(predicate);
customerQuery.select(customerRoot).where(customerRoot.get("id").in(subQuery));
em.createQuery(issueQuery).getResultList();