ALTER TABLE添加ON DELETE CASCADE语句 [英] ALTER TABLE to add ON DELETE CASCADE statement

问题描述

我想在PostgreSQL中执行以下操作（使用Hibernate）：

  ALTER TABLE果实ADD CONSTRAINTS id ON DELETE CASCADE; 
  

显然，我上面的代码不工作，所以我在寻找正确的语句。

如果我不能这样做，那么以下情况如何：

我的表中有一堆数据水果。 fruits 中的 id 字段被表 grapes 。我需要删除 fruits 中的特定行，并且希望删除级联到 grapes ，并删除葡萄，它具有指定的 id 。如何做到这一点？

 从水果中删除其中id = 1级联; 
  

注意：我不想进行连接并删除<$ c $中的相应数据C>葡萄。这只是一个例子。在实际的应用程序中，大量的表依赖于 fruits 。

因为我使用Hibernate，当我使用delete语句时，hibernate可以帮忙吗？

或者我可以用PostgreSQL中的信息模式或系统目录来做到这一点吗？

解决方案

我找到了答案：

  //在Fruit对象中
 @OneToMany （mappedBy =fruit，orphanRemoval = true）
 private List< Grape>葡萄; 
 
 //在Grape对象中
 @OneToOne 
私有水果; 
  

I want to do the following in PostgreSQL (using Hibernate):

 ALTER TABLE fruits ADD CONSTRAINTS id ON DELETE CASCADE;

Obviously, my code above is not working, so I am looking for the correct statement.

If I can't do that, then how about the following:

I have a bunch of data in my table fruits. The id field in fruits is used as a foreign key by table grapes. I need to delete a specific row in fruits and I want the deletion to cascade to grapes and delete all entries in grapes that has the specified id. How do I do that?

delete from fruits where id = 1 cascade; 

NOTE: I don't want to do a join and delete the corresponding data in grape. This is just an example. In the real application a large number of tables depend on fruits.

Since I am using Hibernate, for the case when I use a delete statement, can hibernate help do it?
Or can I do this with the information schema or system catalog in PostgreSQL?

解决方案

I found the answer:

    //in Fruit object
    @OneToMany(mappedBy = "fruit", orphanRemoval=true)
    private List<Grape> grapes;

   //in Grape object
   @OneToOne
   private Fruit fruit;

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