JPA JoinColumn属于该成员实体后面的表的外键 [英] JPA JoinColumn for foreign keys belonging to the table behind its member entity

问题描述

我有表 table_a 和 table_b 和外键 table_a_id 在 table_a 中引用主键 id 。

现在我有两个JPA实体， A 和 B 。 A 包含对 B 的引用。

  public class A {
 
 ... 
 
 @JoinColumn（name =table_a_id）
 private B b; 
 
 
 $ 
 
 
 
这会抛出异常，表示列 table_a_id 不能在 table_a 中找到。我知道JPA在 table_a 中寻找一个外键 table_a_id ，但是如何解决这个问题而不移动外键 table_a ？
解决方案 
 @ code> A 和 @JoinColumn 在 B 中。关系的拥有方是外键，在这种情况下是 B 。 mappedBy中的a是类 B中类型 A  / code>。
 
 
 
 编辑  
 
 
 ，当外键在目标表中时，根据这个，如果你把 insertable = false 和 updateable = false  @JoinColumn  JPA提供程序在目标表中查找外键。
 
I have tables table_a and table_b and foreign key table_a_id references the primary key id in table_a.

Now I have two JPA entities, A and B. A contains a reference to B.
public class A {

    ...

    @JoinColumn(name="table_a_id")
    private B b;
}
This throws exceptions saying that column table_a_id cannot be found in table_a. I know JPA is looking for a foreign key table_a_id in table_a but how can I resolve this problem without moving the foreign key to table_a?
解决方案
You can have @OneToOne(mappedBy = "a") in A, and @OneToOne with @JoinColumn in B. The owning side of the relationship is the one where foreign key is, that would be B in this case. "a" in mappedBy is the name of the field of type A in class B.

EDIT

In case of unidirectional relationship, when foreign key is in target table, according to this, if you put insertable = false and updateable = false in @JoinColumn, that will instruct the JPA provider to look for foreign key in the target table.

                        
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