LINQ条件在哪里过滤

Question

Im using ASP MVC, I have this LINQ to get employees DTR:

 IEnumerable<DatatablesViewModel> viewmodel = 
     (from a in db.tHREmployees
      join b in db.tTADTRs on a.EmpID equals b.EmpID
      join c in db.tHRJobGrades on a.JobGrdID equals c.JobGrdID
      join d in db.tTAShifts on b.ShftID equals d.ShftID
      join e in db.tTADays on b.DayID equals e.DayID
      where (b.LogDt >= PeriodDates.FromDt && b.LogDt <= PeriodDates.ToDt)
      select new DatatablesViewModel
      {
          EmpID = a.EmpID,
          Name = a.LastNm + ", " + a.FirstNm + ", " + a.MiddleNm,
          JobGradeDesc = c.JobGrdDesc,
          ShftNm = d.ShftNm,
          DayType = e.DayNm,
          LogDT = b.LogDt,
          LogIn = b.LogIn,
          LogOut = b.LogOut,
          Absent = b.AbsDay,
          Work = b.WorkHr,
          Late = b.LateHr,
          Overtime = b.OTHr,
          Undertime = b.OTHr,
          Nightdiff = b.NDHr,
          NightPrem = b.NPHr,
          ApprovedOT = b.AppOT,
          ApprovedOB = b.AppOB,
          ApprovedCoa = b.AppCOA,
          ApprovedCs = b.AppCS,
          Exception = b.ExcptStatus
      }).OrderBy(x => x.EmpID);

In my view i have dropdown menu that has employee names with 'ALL' option. I want to add a condition inside 'where' in above code somthing like:

if(parameter.selectedEmp != "ALL"){
Where(x => x.EmpID == param.CustomParam_EmpID) <-- add this filter

}

I want to select only what is needed in my query to avoid delay.

Answer 1

You don't need to add it in the Where clause directly. The IEnumerable and your LINQ query are only evaluated once you start to iterate through the collection. You could simply do something like this:

var relevantVMObjects = 
 (from a in db.tHREmployees
  join b in db.tTADTRs on a.EmpID equals b.EmpID
  join c in db.tHRJobGrades on a.JobGrdID equals c.JobGrdID
  join d in db.tTAShifts on b.ShftID equals d.ShftID
  join e in db.tTADays on b.DayID equals e.DayID
  where (b.LogDt >= PeriodDates.FromDt && b.LogDt <= PeriodDates.ToDt)
  select new DatatablesViewModel
  {
      EmpID = a.EmpID,
      Name = a.LastNm + ", " + a.FirstNm + ", " + a.MiddleNm,
      JobGradeDesc = c.JobGrdDesc,
      ShftNm = d.ShftNm,
      DayType = e.DayNm,
      LogDT = b.LogDt,
      LogIn = b.LogIn,
      LogOut = b.LogOut,
      Absent = b.AbsDay,
      Work = b.WorkHr,
      Late = b.LateHr,
      Overtime = b.OTHr,
      Undertime = b.OTHr,
      Nightdiff = b.NDHr,
      NightPrem = b.NPHr,
      ApprovedOT = b.AppOT,
      ApprovedOB = b.AppOB,
      ApprovedCoa = b.AppCOA,
      ApprovedCs = b.AppCS,
      Exception = b.ExcptStatus
  }).OrderBy(x => x.EmpID);

 if(parameter.selectedEmp != "ALL")
      relevantVMObjects = relevantVMObjects.Where(x => x.EmpID == param.CustomParam_EmpID);
 IEnumerable<DatatablesViewModel> viewmodel = relevantVMObjects;

Answer 2

You can do this by OR condition

string selectedEmp=parameter.selectedEmp;
IEnumerable<DatatablesViewModel> viewmodel = 
     (from a in db.tHREmployees
      join b in db.tTADTRs on a.EmpID equals b.EmpID
      join c in db.tHRJobGrades on a.JobGrdID equals c.JobGrdID
      join d in db.tTAShifts on b.ShftID equals d.ShftID
      join e in db.tTADays on b.DayID equals e.DayID
      where (b.LogDt >= PeriodDates.FromDt && b.LogDt <= PeriodDates.ToDt) &&
      (selectedEmp != "ALL" || a.EmpID == param.CustomParam_EmpID)
 select new DatatablesViewModel
      {
           ...
      }