c# 左连接写法

var itemandformulas =
                     from i in AttendanceItemList
                     join f in AttendanceFormulaList
                     on i.AttendanceCode equals f.ItemCode into itemandformula
                     from formula in itemandformula.DefaultIfEmpty()
                     select new
                     {
                         i.IsShouldSpent,
                         i.InUse,
                         i.AttendanceCode,
                         formula,
                     };

                foreach (var attenitem in itemandformulas)
                {

                     attenitem.formula 为第二个list里的 内容

                }

AttendanceItemList left  join AttendanceItemList on  i.AttendanceCode =f.ItemCode into itemandformula

join 链接

foreach (var update in AttendanceItemList.Join(AttendanceFormulaList,
                         (l) => { return l.AttenceCode; },
                         (e) => { return e.ItemCode; },
                         (l, e) => new { l, e }))
                    {

                    }

可以下载一个 linqpad学习一下.

http://www.cnblogs.com/Mayvar/archive/2011/07/04/wanghonghua_201107040534.html