SQL:一个外键引用几个表之一中的主键 [英] SQL : one foreign key references primary key in one of several tables

问题描述

我正在开发一个应用程序，该应用程序将用作其他应用程序的可扩展框架.

I am working on an application that will be used as an extensible framework for other applications.

其中一个基本类称为 Node，Node 具有 Content.SQL 表如下所示:

One of the fundamental classes is called Node, and Nodes have Content. The SQL tables look like this:

TABLE 节点(NodeId int, .... 等)

TABLE Node ( NodeId int, .... etc )

TABLE NodeContentRelationship (NodeId int, ContentType string, ContentId int)

TABLE NodeContentRelationship ( NodeId int, ContentType string, ContentId int)

这将取决于扩展应用程序以创建自己的内容类型的开发人员.

It will be up to the developers extending the application to create their own content types.

显然，从关系数据库的角度来看，这很糟糕，因为无法将外键关系添加到 NodeContentRelationship.ContentId，即使它是一个外键列.

Clearly this is bad from a relationship-database point of view as it is not possible to add a foreign key relationship to NodeContentRelationship.ContentId, even though it is a foreign key column.

但是，解决方案非常简单且功能强大，因此我不愿意更改它.

However, the solution is quite simple and powerful so I am reluctant to change it.

你怎么看 - 我会在赛道上陷入痛苦的世界吗?

What do you think - am I in for a world of pain down the track?

推荐答案

为什么不能设置NoteContentRelationship.ContentId为外键?您可以轻松地使用关系继承模型，其中表 Content 表示抽象基类，各种表 AnimalContent、CarContent 等表示派生类.

Why is it impossible to set NoteContentRelationship.ContentId as a foreign key? You can easily use a relational inheritance model with a table Content representing an abstract base class, and various tables AnimalContent, CarContent, etc. representing derived classes.

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