How to convert datetime to date in linq query in nopcommerce c#

Question

 query = (from s in _studentRepository.Table
     //from a in _attendanceRepository.Table.Where(j => j.StudentId == s.Id && (j.Date == date.Date)).DefaultIfEmpty()
     from a in _attendanceRepository.Table.Where(j => j.StudentId == s.Id).DefaultIfEmpty()
     where s.ClassSectionId == searchClassSectionId && (a.Date == Convert.ToString(date, "DD/MM/YYYY") || a.Date == null)
     select new
     {
         AttendanceTypeId = (a != null ? a.AttendanceTypeId : 0),
             Date = (a != null ? a.Date : default(DateTime)),
             Id = (a != null ? a.Id : 0),
             Student = s
     }).ToList().Select(x => new Attendance()
     {
         Id = x.Id,
         AttendanceTypeId = x.AttendanceTypeId,
         Date = x.Date,
         Student = x.Student
     }).ToList();

Answer 1

Your problem is that formatting doesn't belong in the Linq query itself. The query is concerned with data, not presentation. This is happening because LINQ to Entities is trying to convert the expression tree into SQL query and .ToString(string) can not be translated into SQL. then make sure you enumerate the collection before doing your formatting. You can call .ToList(), or you can use range date.

I think the following code can help you

query = (from s in _studentRepository.Table
                     //from a in _attendanceRepository.Table.Where(j => j.StudentId == s.Id && (j.Date == date.Date)).DefaultIfEmpty()
                 from a in _attendanceRepository.Table.Where(j => j.StudentId == s.Id).DefaultIfEmpty()
                 where s.ClassSectionId == searchClassSectionId && (a.Date >= DateTime.Parse(date.ToString(CultureInfo.InvariantCulture)).Date 
                 && a.Date < DateTime.Parse(date.ToString(CultureInfo.InvariantCulture))
                 .Date.AddDays(1).AddTicks(-1) || a.Date == null)
                 select new
                 {
                     AttendanceTypeId = (a != null ? a.AttendanceTypeId : 0),
                     Date = (a != null ? a.Date : default(DateTime)),
                     Id = (a != null ? a.Id : 0),
                     Student = s
                 }).ToList().Select(x => new Attendance()
                 {
                     Id = x.Id,
                     AttendanceTypeId = x.AttendanceTypeId,
                     Date = x.Date,
                     Student = x.Student
                 }).ToList();