如何通过实体键添加/删除与实体框架的多对多关系？

I tried:

using (Entities e = new Entities())
{
    EntityKey key = new EntityKey("Entities.Users", "UserId", 20);
    User user = new User { EntityKey = key};
    Role role = e.Roles.FirstOrDefault();
    //role.Users.Attach(user); //throws (when uncommented...) InvalidOperationException:
    //The object being attached to the source object is not attached to the same ObjectContext as the source object.
    role.Users.Add(user); //throws InvalidOperationException too:
    //The object cannot be added to the ObjectStateManager because it already has an EntityKey. Use ObjectContext.Attach to attach an object that has an existing key.
    e.SaveChanges();
}

当尝试使用Remove()而不调用attach时，不会引发异常但关系不会被删除。

尝试这样的事情：

User user = new User {UserId = 20};
e.AttachTo("Users", user);
Role role = e.Roles.FirstOrDefault();
role.Users.Add(user);
e.SaveChanges();

我发现使用存根实体（如上面的用户）比使用 EntityKey 更容易。

看到这个博客文章 http://blogs.msdn.com/alexj/archive/2009/06/19/tip-26-how-to-avoid-database-queries-using-stub-entities.aspx有关存根实体技术的更多信息。

希望这可以帮助

Alex