Hibernate外键与复合主键的一部分 [英] Hibernate foreign key with a part of composite primary key

问题描述

我必须使用Hibernate，我不太清楚如何解决这个问题，我有两个表，1..n关系像这样：

 
 ------- 
 TABLE_A 
 ------- 
 col_b（pk）
 col_c（pk）
 [其他字段] 
 
 ------- 
 TABLE_B 
 ------- 
 col_a （pk）
 col_b（pk）（fk TABLE_A.col_b）
 col_c（fk TABLE_A.col_c）
 [其他字段] 
 

我如何用Hibernate来管理它？

我不知道如何声明一个包含主要部分的外键key。

我的数据库模式是从Hibernate模型生成的。 我已经找到了解决这个问题的两个解决方案。

第一个解决方法是一个解决方法，不像第二个解决方案那么简单。 b

将 B 实体的主键定义为包含 col_a ， col_b 和 co l_c ，首先应该是主键，定义为唯一约束。缺点是列 col_c 在概念上并不是主键的一部分。

  @Entity 
 class A {
 @Id 
 private int b; 
 @Id 
 private int c; 
 
 $ b $实体
 @Table（uniqueConstraints = {@UniqueConstraint（columnNames = {a，b}）}）
 class B {
 @Id 
 private int a; 
 
 @Id 
 @ManyToOne（可选= false）
 @JoinColumns（value = {
 @JoinColumn（name =b，referencedColumnName =b） ，
 @JoinColumn（name =c，referencedColumnName =c）}）
 private一个entityA; 
 
 
 
 
 
 
第二个使用 @EmbeddedId 和 @MapsId 注释，并且完全是我最初想做的事情。 
 
 
  @Entity 
 class A {
 @Id 
 private int b; 
 @Id 
 private int c; 
} 
 
 @Embeddable 
 class BKey {
 private int a; 
 private int b; 
} 
 
 @Entity 
 class B {
 @EmbeddedId 
 private BKey primaryKey; 
 
 @MapsId（b）
 @ManyToOne（可选= false）
 @JoinColumns（value = {
 @JoinColumn（name =b，referencedColumnName =b），
 @JoinColumn（name =c，referencedColumnName =c）}）
 private一个entityA; 
} 
  
 


I have to work with Hibernate and I am not very sure how to solve this problem, I have 2 tables with a 1..n relationship like this:
-------
TABLE_A
-------
col_b (pk)
col_c (pk)
[other fields]

-------
TABLE_B
-------
col_a (pk)
col_b (pk) (fk TABLE_A.col_b)
col_c (fk TABLE_A.col_c)
[other fields]
How can I manage this with Hibernate?


I do not have any idea how to declare a foreign key that would contain a part of primary key.

My database schema is generated from the Hibernate model.
解决方案
I have found two solutions to this problem.

The first one is rather a workaround and is not so neat as the second one.

Define the primary key of the B entity as composite key containing col_a, col_b, and col_c and what was supposed to be the primary key in the first place, define as unique constraint. The disadvantage is that the column col_c is not really conceptually a part of primary key.
@Entity
class A {
  @Id
  private int b;
  @Id
  private int c;
}

@Entity
@Table(uniqueConstraints = {@UniqueConstraint(columnNames = { "a", "b" }) })
class B {
  @Id
  private int a;

  @Id
  @ManyToOne(optional = false)
  @JoinColumns(value = {
          @JoinColumn(name = "b", referencedColumnName = "b"),
          @JoinColumn(name = "c", referencedColumnName = "c") })
  private A entityA;
}
The second uses @EmbeddedId and @MapsId annotations and does exactly what I wanted to be done at the very beginning.
@Entity
class A {
  @Id
  private int b;
  @Id
  private int c;
}

@Embeddable
class BKey {
  private int a;
  private int b;
}

@Entity
class B {
  @EmbeddedId
  private BKey primaryKey;

  @MapsId("b")
  @ManyToOne(optional = false)
  @JoinColumns(value = {
          @JoinColumn(name = "b", referencedColumnName = "b"),
          @JoinColumn(name = "c", referencedColumnName = "c") })
  private A entityA;
}


                        
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