关于 JPQL 的问题，@NamedQuery
如果我有类似的东西，
@Entity
public class Facility {
...
@ManyToOne
@JoinColumn(name="CUSTOMER_FK")
private Customer customer;
...
}
我的 @NameQuery 会像这样
@NamedQuery(name="Facility.findByCustomerId", query="select c from Facility c where c.customer=:customer_fk")
或这样
@NamedQuery(name="Facility.findByCustomerId", query="select c from Facility c where c.CUSTOMER_FK=:customer_fk")
If I have something like this
@Entity
public class Facility {
...
@ManyToOne
@JoinColumn(name="CUSTOMER_FK")
private Customer customer;
...
}
does my @NameQuery like this
@NamedQuery(name="Facility.findByCustomerId", query="select c from Facility c where c.customer=:customer_fk")
or like this
@NamedQuery(name="Facility.findByCustomerId", query="select c from Facility c where c.CUSTOMER_FK=:customer_fk")
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使用 JPQL 时，您需要停止考虑外键并开始考虑对象。让我们仔细看看：
您的
Facility是否有CUSTOMER_FK财产？不，所以上面的查询是不正确的。下一篇：从语法上看，这个是正确的。但你仍然没有思考对象。在这里，查询希望您传递客户实例，而不是 FK。因此，我会像这样重写它（它是相同的查询，但它更好地传达了IMO的意图，而且我实际上会避免任何
foo_fk约定，你不真正使用 JPA 操作 FK）：如果您确实想通过 id 查找，您应该浏览关联并编写：
You need to stop thinking foreign keys and to start thinking object when using JPQL. Let's take a closer look:
Does your
Facilityhave aCUSTOMER_FKproperty? No, so the above query is incorrect. Next one:Syntacticly, this one is correct. But you're still not thinking object. Here, the query expect you to pass an instance of customer, not a FK. I'd thus rewrite it like this (it is the same query but it communicates IMO the intention much better and I'd actually avoid any
foo_fkconvention, you don't really manipulate FK with JPA):And if you really want to find by id, you should navigate through the association and write:
在 JPQL 中，您使用属性的名称，而不是数据库列。所以 - 第一个选择。
但是当您传递参数时，您传递的是整个对象，而不是它们的 ID。在您的情况下，您可以传递
Customer实例，或者使 where 子句查找c.customer.id（并且您最好将别名命名为f，而不是c）In JPQL you use the names of the properties, not the database columns. So - the first option.
But when you pass parameters, you pass the whole objects, not their IDs. In your case, you either pass a
Customerinstance, or make the where clause look forc.customer.id(and you'd better name the aliasf, notc)