如何在几个表上设置一个FK（外键）？ [英] How to set one FK (foreign key) on several tables?

问题描述

我有几个帖子表和一个表决表。如何防止在投票中插入不存在的 post_id （在 / code>表？

  // Posts_1 // Posts_2 // Posts_3 
 + + --------- + + ---- + --------- + + ---- + --------- + 
 | id |内容| | id |内容| | id |内容| 
 + ---- + --------- + + ---- + --------- + + ---- + -------- -  + 
 
 //投票
 + ---- + --------- + 
 | id | post_id | 
 + ---- + --------- + 
  

应该注意，实际上 Posts 表的结构不同。 （所有 Posts 表具有不同的结构），然后我不能将所有 posts 表合并为一个表。 / p>



现在我想防止在 Votes 表中插入无效行。 （无效= post_id 不存在于帖子表中）

所以，如果我只有一个表，我可以在 Votes.post_id 上创建一个外键 Posts.id ，但问题是有几个 posts 表。好的，有什么建议吗？

解决方案

表结构是疯狂的。你需要一个POST索引表，它将所有的帖子合并到一个地方，并给出如下：

  // Posts_Index 
 + ---- + --------- + ------------ + 
 | id | post_id | post_table | 
 + ---- + --------- + ------------ + 
 
 //投票
 +  - --- + --------- + 
 | id | post_id | 
 + ---- + --------- + 
  

你需要反向映射的方式。所以， post_id - > votes.id 。

I have several Posts tables and one Votes table. How can I prevent inserting non-existing post_id (in Posts tables) in the Votes table?

// Posts_1                  // Posts_2                  // Posts_3
+----+---------+            +----+---------+            +----+---------+
| id | content |            | id | content |            | id | content |
+----+---------+            +----+---------+            +----+---------+

// Votes
+----+---------+
| id | post_id |
+----+---------+

It should be noted, in reality the structure of Posts tables is different. (all Posts tables have not the same structure), Then I can not combine all Posts tables as one table.

Now I want to prevent of inserting invalid rows in the Votes table. (invalid = post_id is not exist in the none of Posts tables)

So, If I have just one table, I can create a foreign key on the Votes.post_id reference to Posts.id, But the problem is having several Posts table. ok, well, Is there any suggest?

解决方案

The table structure is crazy. You need to have a POST Index Table, which combines all the posts to one single place and gives it like this:

// Posts_Index
+----+---------+------------+
| id | post_id | post_table |
+----+---------+------------+

// Votes
+----+---------+
| id | post_id |
+----+---------+

Else you need to reverse map the way. So that, post_id -> votes.id.

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