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问题描述
我想设置一个外键给一个默认的成员表，但是当我尝试定义它的时候出现错误。我使用默认的aspnet_Users表和我自己的Posts表。我试图设置表如下：
aspnet_Users
错误消息是完全描述的情况 - 你试图在外键约束内使用非关键字段。您建议尝试创建一个组合键来解决这个问题，这将是可行的，但为什么不简单地使用现有的主键？
UserID字段是一个唯一标识符PK，所以它已经被配置为在FK中使用。而且，你会利用规范化，所以不是每个用户在每行存储（最多）256字节，而只是存储uniqueidentifier（16字节）。
I'd like to setup a foreign key to a default membership table but I'm getting an error when trying to define it. I'm using the default aspnet_Users table and also my own Posts table. I'm trying to setup the tables as follows:
aspnet_Users
- UserId (PK) uniqueidentifier
- UserName nvarchar(256)
Posts
- PostID (PK) int
- UserName (FK -> aspnet_Users.UserName) nvarchar(256)
However, when I try to set this up using the VS 2010 designer, it gives me the following error:
The columns in table 'aspnet_Users' do not match an existing primary key
or unique constraint.
Is this not working because aspnet_Users.UserName isn't a part of the PK for aspnet_Users? I've tried to change the table to include that as part of the PK (I think that makes it a composite key?) but it's telling me to delete the relationships first before I can do it. Being as I don't know what relationships the default membership tables define, I'd rather find out more before going that route.
解决方案
The error message is fully describing the situation - you're trying to use a non-key field inside a foreign key constraint. You suggest trying to create a composite key to get around this issue, which would work, but why wouldn't you simply use the existing primary key?
The UserID field is a uniqueidentifier PK, so it is already configured for use in a FK. And, you'd be utilizing normalization, so that rather than storing (up to) 256 bytes per Username on each row, you'd only be storing the uniqueidentifier (16 bytes).
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