如何在此lambda表达式中指定“not in”？

Question

我有一个快速的问题，因为我的大脑不能和我一起工作......
我在哪里指定我希望'Users'中的user_id不在'Groups'中？

db.Users.Join(db.Groups, a => a.user_id, b => b.user_id, (a, b) => new SelectListItem
{
  Value = a.user_id.ToString(),
  Text = a.surname + " " + a.lastname
});

Answer 1

以下应该有效（假设我正确理解了您的问题）：

db.Users
.Where(x => !db.Groups.Any(y => y.user_id == x.user_id))
.Select(a => new SelectListItem
    {
        Value = a.user_id.ToString(),
        Text = a.surname + " " + a.lastname
    });

Answer 2

你可以尝试这样的事情：

var query =  from u in db.Users
             where !(from g in dc.Groups
                     select g.user_id)
                     .Contains(u.user_id)
             select new SelectListItem { 
                         Value = u.user_id.ToString(),
                     Text = u.surname + " " + u.lastname
         };

看看这里： http ： //introducinglinq.com/blogs/marcorusso/archive/2008/01/14/the-not-in-clause-in-linq-to-sql.aspx