定义列表的顺序 [英] Defining the order of a list

问题描述

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。我想要完成的是将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 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?

我正在使用EclipseLink作为我的JPA提供商。

I'm using EclipseLink as my JPA provider.

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;
}

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。

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".

推荐答案

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可能甚至不是为了检索你的b而发出的选择的一部分。

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.

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