Linq to SQL 插入数据时的一个问题

代码如下:

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 

复制代码代码如下:

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。