关于关联的 Hibernate 自定义连接子句 [英] Hibernate custom join clause on association

问题描述

我想使用休眠注释将 2 个实体与自定义连接子句相关联.该子句涉及通常的 FK/PK 相等，但也涉及 FK 为空的情况.在 SQL 中，这将类似于:

join b on a.id = b.a_id 或 b.a_id 为空

从我读到的内容来看，我应该在所有者实体上使用 @WhereJoinTable 注释，但我对如何指定这个条件感到困惑……尤其是它的第一部分 - 指的是加入实体的 id.

有人举个例子吗?

解决方案

这是一个使用标准父/子范式的示例，我认为应该使用基本的 @Where 注释.

公共类 A {...@ManyToOne(fetch = FetchType.EAGER)//EAGER 强制外连接@JoinColumn(name = "a_id")@Where(clause = "a_id = id or a_id is null")//id"是A的PK...根据需要修改公共 B getB() { 返回 b;}}公共类 B {...@OneToMany(mappedBy = "b")公共列表<A>getA() { 返回一个；}}

I would like to associate 2 entities using hibernate annotations with a custom join clause. The clause is on the usual FK/PK equality, but also where the FK is null. In SQL this would be something like:

join b on a.id = b.a_id or b.a_id is null

From what I have read I should use the @WhereJoinTable annotation on the owner entity, but I'm puzzled about how I specify this condition...especially the first part of it - referring to the joining entity's id.

Does anyone have an example?

解决方案

Here's an example using the standard parent/child paradigm that I think should work using the basic @Where annotation.

public class A {
  ...
  @ManyToOne(fetch = FetchType.EAGER) // EAGER forces outer join
  @JoinColumn(name = "a_id")
  @Where(clause = "a_id = id or a_id is null") // "id" is A's PK... modify as needed
  public B getB() { return b; }

}

public class B {
  ...
  @OneToMany(mappedBy = "b")
  public List<A> getA() { return a; }
}

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