实体框架生成不适当的查询

Question

I am using EntityFramework 4. I am facing strange issue with entity framework, here is the code:

public void UpdateLink(Link link)
{
     Link existing = ObjectContext
                    .Link
                    .FirstOrDefault(p => p.ItemLeft == link.ItemLeft 
                                      && p.ItemRight == link.ItemRight 
                                      && p.DeleteTime == null);

    if (existing != null)
    {
        existing.DeleteTime = link.DeleteTime;
    }

    ObjectContext.SaveChanges();
}

Let's say existing item is found and DeleteTime is set for this item. (if statement was passed)

Then when SaveChanges is called I get query (with sql profiler) wich updates all the records where ItemLeft is X and ItemRight is Y. In fact it ignores DeleteTime = null condition...

Looks like that:

exec sp_executesql N'update [Link] set [DeleteTime] = @0
where (([ItemLeft] = @1) and ([ItemRight] = @2))
',N'@0 datetime,@1 int,@2 int',@0='2013-04-23 14:58:21.853',@1=857,@2=872

Table structure:

ID [PK]
(index)LeftItem int
(index)RightItem int
(index)DeleteTime datetime?

What am I missing? please help!

Answer 1

In theory, the update generated base itself on the primary key of the entity.

So your context must have fired in fact two queries:

1. A SELECT TOP 1 with the WHERE clause you give
2. An update query WHERE Id = entity.Id

The generated query looks very weird, so the main problem is certainly that you don't have a primary key define on your table.
Another solution is that the mapping between your database and your ObjectContext is totally screwed. Check the implementation of the Link class.

Answer 2

Thanks to Scorpi0 and Maarten. Such problems may arise when table does not contains primary key or there are some primary key differences between context entity and database table