linq的常用写法

1.DataTable

        DataTable dt = udb.GetAllUser();
        DataTable dt1 = new DataTable();

        IEnumerable<DataRow> q1 = from r in dt.AsEnumerable()

                                  where r.Field<int>("车间ID") == Convert.ToInt32(车间ID) && r.Field<int>("IsAdmin") == 0
                                  orderby r.Field<int>("车间ID") ascending
                                  select r;
        dt1 = q1.CopyToDataTable();

r.Field<int>("车间ID") 这么写也行Convert.ToInt32(r["车间ID"])

2.List

                List<DIC_RELA_RAILLINE_NODE> SelectGet =
                (from x in DIC_RELA_RAILLINE_NODEs
                 where x.SUB_LINE_ID == RailTrackLines[i].R_ID.ToString()
                 orderby x.Center_kilo ascending
                 select x).ToList();

3.对象关联

        var result = from x in SUIs

           from y in SUs

                     where x.JobNumber != y.JobNumber && y.DispatchID == "1"

           select new {

               Name = x.Name,

               Title = x.Name,

               Body = x.Name,

           };

或者

        List<Sale_UserInterface> result =
            (from x in SUIs
             from y in SUs
             where x.JobNumber != y.JobNumber && y.DispatchID == "1"
             select x).ToList();

 

 

分页的写法

        IEnumerable<DataRow> q1 = (from r in dt.AsEnumerable()

                                  orderby r.Field<int>("ID") ascending
                                   select r).Skip(startIndex - 1).Take(pageSize);

Skip和Take

 

用var

var q1 = (from r in CUs                  

orderby r.CreateTime ascending                  

select r).Skip(startIndex - 1).Take(pageSize);

List<Common_User> CUs2 = new List<Common_User>();         CUs2 = q1.ToList();

 

 

        var query = from l in 色彩s
                    group l by new { l.色彩ID } into g
                    select new
                    {

                        色彩ID = g.Key.色彩ID,
                        Score = g.Sum(o => o.Score)
                    };

double q = db.MenuInfo.Where(p => p.PID == PID).Max(p => p.IOrder);