与连接表的一对多关系 [英] One-To-Many Relationship with Join Table

问题描述

我有一个使用连接表建模的一对多关系：

I have a one-to-many relationship modeled using join table:

create table t1 (id int primary key, name varchar(10) /*...*/);
create table t2 (id int primary key, name varchar(10) /*...*/);
create table t1_t2 (t1_id int, t2_id int, primary key (t1, t2));

这些表应该模拟一个t1到多个t2的关系。使用JPA对这些表进行建模的正确方法是什么？

The tables are supposed to model the relationship of one t1 to many t2. What is the right way to model these tables using JPA?

推荐答案

一个T1到多个T2的典型表格是T2上的外键指向T1。通常不需要T1_T2表。

The typical table for one T1 to many T2 is to have a foreign key on T2 pointing toward T1. The T1_T2 table is usually not needed.

JPA结构将是一对多，可能是双向的。

The JPA structure would then be a One-To-Many, possibly two-way.

为了使你描述的结构有效，可能会有一些安排。你可以改变T1_T2：

There could be some arrangements, to make the structure you describe work. You could change T1_T2:

• 在T2上添加一个唯一约束（这样只允许一个T2）

这真的是你想要的吗？

已编辑：是的，它是你想要什么; - ）

Edited: yes, it is what you want ;-)

我怀疑你可能在网上找到很多例子。我没有经证实的解决方案，但我会尝试这些方法：

I doubt you may find many examples on the net. I have no proved solution, but I would try something along these lines:

在 Hibernate注释参考文档，参见2.2.5.3.2.3。带有连接表的单向获取这个想法。它看起来像：

In Hibernate annotation reference documentation, see "2.2.5.3.2.3. Unidirectional with join table" to get the idea. It looks like:

    @Entity
    public class Trainer {
        @OneToMany
        @JoinTable(
            name="TrainedMonkeys",
            joinColumns = @JoinColumn( name="trainer_id"),
            inverseJoinColumns = @JoinColumn( name="monkey_id")
        )
        public Set<Monkey> getTrainedMonkeys() {
        ...
    }

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