如何在hibernate中使用单个表连接三个表？ [英] How to join three tables using a single table in hibernate?

问题描述

我有三张桌子 A ， B 和 C 和一个映射表 A_B_C ，其中包含所有三个表和一些其他属性的外键（假设 X ， ý）。现在，我想加入在我的java类中表示这三个表。

I have three tables A, B and C and a mapping table A_B_C which has foreign keys to all the three tables and some other attributes (let's say X,Y). Now, I want to join represent these three table in my java class.

这些表之间的关系是一对多的。因此，我希望我的Java类看起来像这样。

The relationship between these tables are one to many. Hence, I want my Java classes to look something like this.

@Entity(name = "A")
@Table(name = "A")
public class A {

       ??? Hibernate Annotation or query
       Map<B,List<C>> BMapC;
}

@Entity(name = "B")
@Table(name = "B")
public class B {
      ...
}

@Entity(name = "C")
@Table(name = "C")
public class C {
      ...
}

我想知道是否可以利用Hibernate Annotations 。如果没有，有没有办法可以编写自定义查询并填充变量？

I would like to know if it would be possible to leverage Hibernate Annotations for this. If not, is there a way I can write a custom query and populate the variable?

推荐答案

不幸的是，hibernate没有为这种情况提供开箱即用的任何注释。此方案只能通过创建映射到 A_B_C 的类来处理：

Unfortunately hibernate does not provide any annotations out-of-the-box for such scenarios. This scenario can only be handled by creating a class mapping to A_B_C :

@Entity
@Table(name = "A_B_C")
public class name = "A_B_C" {

     @ManyToOne(cascade=CascadeType.ALL)
     @JoinColumn(name = "FK_B", nullable = false)
     private B b;

     @ManyToOne(cascade=CascadeType.ALL)
     @JoinColumn(name = "FK_C", nullable = false)
     private C c;

     //Getters, Setters, other attributes etc.
} 

并在A中有一个这个对象的列表：

And have a list of this object in A:

 @Entity
 @Table(name = "A")
 public class name = "A" {

          @OneToMany(cascade=CascadeType.ALL)
          @JoinColumn(name = "FK_A", nullable = false)
          private Set<A_B_C> abc;

          //Getters, Setters, other attributes etc.
 } 

以编程方式将Set abc转换为 B，C 的地图。

And programmatically convert the Set abc to a map of B,C.

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