定义列表的顺序

I have the following problem. I have three classes, A, B and C. A contains a OneToMany relationed list of B:s. B contains a ManyToOne relation to C. C contains a field called "name" and B also contains a field called "name". What I'd like to accomplish is to have the items in A's list sorted primarily by C's name and secondarily by B's name - the problem is that I do not know how to do this. Is it even possible?

我有以下问题。我有三个类,A,B和C. A包含一个关于B:s的OneToMany关系列表。 B包含与C的ManyToOne关系.C包含名为“name”的字段,B还包含名为“name”的字段。我想要完成的是让A列表中的项目主要按C的名称排序,其次按B的名称排序 - 问题是我不知道如何做到这一点。它甚至可能吗?

I'm using EclipseLink as my JPA provider.

我正在使用EclipseLink作为我的JPA提供程序。


class A {
   @OneToMany
   @OrderBy("b.c.name, b.name") <---- this is the problem
   List<B> b;
}

class B {
   @ManyToOne
   C c;
   String name;
}

class C {
   String name;
}

EDIT Yes, I've tried different variations, for example @OrderBy("c.name") doesn't work, I just get an error message telling me that the entity class b does not contain a field called "c.name".

编辑是的,我尝试了不同的变体,例如@OrderBy(“c.name”)不起作用,我只是收到一条错误消息,告诉我实体类b不包含名为“c.name”的字段。

5 个解决方案

#1

It's NOT possible. @OrderBy only accepts direct property / field names, not nested properties. Which makes sense, really, because "c" table - depending on your fetching strategy may not even be part of a select issued to retrieve your "b"s.

这是不可能的。 @OrderBy只接受直接属性/字段名称,而不接受嵌套属性。这是有道理的,真的,因为“c”表 - 取决于你的提取策略甚至可能不是一个选择的一部分来检索你的“b”。

#2

ChssPly76 is right.

ChssPly76是对的。

What you could do is to create a named query like this one:

你可以做的是创建一个这样的命名查询:

 SELECT b 
 FROM B b 
 WHERE b.a = :mya 
 ORDER BY b.c.name

#3

Have you tried @OrderBy("c.name", "name") ?

你试过@OrderBy(“c.name”,“name”)吗?

You shouldn't use "b." because it's implied that the @OrderBy will be done on columns of the instances of B on the b array.

你不应该使用“b。”因为暗示@OrderBy将在b数组的B实例的列上完成。

#4

Have you tried:

你有没有尝试过:

 @OrderBy("c.name ASC", "name ASC")

#5

It is not possible in javax.persistence.OrderBy (as say ChssPly76 ), but when I was using Hibernate I construct new column in PLAIN SQL with Formula() annotation and then OrderBy over it:

在javax.persistence.OrderBy(如ChssPly76)中是不可能的,但是当我使用Hibernate时,我在PLAIN SQL中使用Formula()注释构建新列,然后使用OrderBy:

class A {
   @OneToMany
   @OrderBy("orderCol") <---- reference to virtual column
   List<B> b;
}

class B {
   @ManyToOne
   C c;
   String name;

   @org.hibernate.annotations.Formula(
     "( select C_table.name as orderCol from C_table where C_table.id = id )"
   ) <------------------------------------------ join with plain SQL statment
   String orderCol;
}

May be EclipseLink has same possibilities?

可能是EclipseLink有相同的可能性吗?

#1

#2