HQL中的内部联接查询

Question

我无法为内部联接执行HQL,查询在sql执行正确但在HQL中执行不正确.我不知道我在哪儿.你的帮助很明显.

 ***Error***: org.hibernate.hql.ast.QuerySyntaxError: unexpected token: ON near line 1, column 148 [SELECT op.username, op.email, orders.p_id, orders.o_id, product.listed_price FROM com.model.Orders  orders INNER JOIN orders.OrderProcessing as op ON op.u_id = orders.u_id INNER JOIN orders.Product as product ON product.p_id = orders.p_id WHERE product.p_id = '208' ORDER BY op.username]

productList = (List<Orders>) session.createQuery(
 "SELECT op.username, op.email, orders.p_id, orders.o_id, product.listed_price " +                                                                               
 "FROM Orders orders " +                                                                   
 "INNER JOIN orders.OrderProcessing as op " +                                                                                       
 "ON op.u_id = orders.u_id " +                                                         
 "INNER JOIN orders.Product as product " +                                                              
 "ON product.p_id = orders.p_id " +                                                        
 "WHERE product.p_id = '"+p_id +"' " +                                                         
 "ORDER BY op.username"
).list();

Answer 1

HQL中的联接语法略有不同.

如果您已经将这些关联映射到Hibernate,则连接条件(id要进行连接的字段)通常由Hibernate本身(已经在映射中定义了该信息)处理,因此您只需要指定哪个属性关联映射,并在其上进行连接:

SELECT op.username, op.email, orders.p_id, orders.o_id, product.listed_price 
FROM Orders order
INNER JOIN order.orderProcessing as op
INNER JOIN order.product as product 
ORDER BY op.username

如果您没有映射这些关联,则应该使用类似语法的交叉连接,并在WHERE子句中指定连接条件.请注意,这可能会对效率产生负面影响,具体取决于您的架构结构和DBMS.

SELECT op.username, op.email, orders.p_id, orders.o_id, product.listed_price
FROM Orders order, OrderProcessing op, Product product
WHERE op.u_id = order.u_id AND product.p_id = orders.p_id
ORDER BY op.username

您可以在14.3中找到有关HQL连接的更多信息.Hibernate参考的关联和连接部分.

Answer 2

加入HQL不像SQL那样工作.你可以加入一个协会:

select order_1.code, item.code, item.quantity 
 from Order order_1 inner join order_1.item item;

或使用多表选择:

select order_1.code, item.code, item.quantity 
 from Order order_1, Item item where item.order=order_1;

任何一种语法都有优点和缺点,所以你应该根据情况选择.

值得注意的是,还有一个隐含的符号,可能根本不需要使用连接:

select item.order.code, item.code, item.quantity from Item item;