Linq to SQL 插入数据时的一个问题

create table rssfeedright
(
feedid int foreign key (feedid) references rssfeed(feedid) not null , -- feedid ,
userid int foreign key (userid) references userinfo(userid) not null , -- userid ,
rightvalue bigint not null primary key (userid, feedid),
)

插入数据的代码

rssfeedright feedright = new rssfeedright();
feedright.userid = userid;
feedright.feedid = feedid;
feedright.rightvalue = 0 ;
_db.rssfeedrights.insertonsubmit(feedright);
_db.submitchanges();
每次插入时都提示说feedid 不能插入空值，郁闷的不行，分明是给了非空值的！
后来仔细检查，发现这个rssfeedright 实体类中居然还有两个指向userinfo 和 rssfeed 表的字段，后来逐渐感觉到是外键设置问题引起的。立即通过google 搜 "linq foreign key insert"
发现有不少人遇到相同问题
找到其中一篇帖子
http://social.msdn.microsoft.com/forums/en-us/linqprojectgeneral/thread/e14f76ec-0ffe-4dd1-893c-6a4c8440c54a
其中关于这个问题是这样描述的
the mapping information (assocation attribute on table1 & table2) has the foreign key dependency going in the wrong direction. it's claiming that the primary-key in table1 (the one that is auto-incremented) is a foreign key to the primary key in table2. you want that just the opposite. you can change this in the designer, dbml file or directly in the code (for a quick test) by changing isforeignkey value for both associations.
也就是说我们不能将主键设置为和外键相同，否则就会出问题。找到问题所在，就好办了，将表结构进行如下修改

create table rssfeedright
(
id int identity ( 1 , 1 ) not null primary key ,
feedid int foreign key (feedid) references rssfeed(feedid) not null , -- feedid ,
userid int foreign key (userid) references userinfo(userid) not null , -- userid ,
rightvalue bigint not null ,
)

问题解决。
老兵遇到新问题，技术不经常更新就要老化。