JPA 2、无实体映射的连接条件查询

Question

我有以下表格：

• 顾客

• 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； 但是我需要一个查询来连接这两个表：

    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();

是否可以使用 JPA 2 执行上述操作？

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();