内部联接的HQL查询和检查NULL失败

Question

我需要选择已链接租用实体的所有客户记录，该实体的字段return_date为null。 以下SQL查询有效：

 SELECT
     c.customer_id, r.rental_id
     FROM
     Customer c
     INNER JOIN rental as r
     ON (c.customer_id = r.customer_id)
     WHERE r.return_date IS NULL;

为什么以下HQL不起作用：

Query query = session.createQuery("from Customer customer " +
                        "inner join customer.rentals as r " +
                        "where r.return_date is null");

语境：

@Override
    public List<Customer> getFilteredCustomers(String filter) {
        Session session = null;
        List<Customer> customers = new ArrayList<>();
            try {
                session = sessionFactory.openSession();
                Query query = session.createQuery("select customer from Customer customer " +
                        "join customer.rentals r " +
                        "where r.return_date is null");
                customers = (List<Customer>)query.list(); // << BREAKPOINT A
            }catch (Exception e){
                System.out.println(e);
            }finally {
                if (session!=null) session.close();
            }
        return customers;
    }

解：

显然，HQL中使用的字段名称必须取自模型类，而不是来自数据库......

Query query = session.createQuery("select c " +
                        " from Rental r, Customer c " +
                        " where r.customer = c " +
                        " and r.returnDate is null");

Answer 1

您的查询不起作用，因为您尝试将客户与集合（租赁）链接，但要在return_date上访问您必须指向集合的i-esime元素，因此您可以反转您的查询，从RENTAL对象开始（我希望您映射了它）

尝试这个：

Query query = session.createQuery("select c " +
           " from Rental r, Customer c " +
           " where r.customer_id = c.customer_id " +
           " and r.return_date is null");