linq in not in
1、not in:lstDown中的DownID属性值不在lstDownfb中的DownID
var lstDown2 = (from d in lstDown
where !(from d2 in lstDownfb select d2.DownID).Contains(d.DownID)
select d).ToList();
2、in:lstDown中的DownID属性值在lstDownfb中的DownID
var lstDown2 = (from d in lstDown
where (from d2 in lstDownfb select d2.DownID).Contains(d.DownID)
select d).ToList();