How to handle null values in linq?

c#, dynamic-list, linq, null, select

Solution

_AttendedDays = new AttendanceBAL()
    .GetAttendanceListOf(q._RollNumber)
    .Where(date => date != null)
    .Select(date => new DateTime(date._Date.Year, date._Date.Month, date._Date.Day))
    .Distinct()
    .ToList(),

The problem is with running `Where()` on null instance. Possible solutions:

1) modify `GetAttendanceListOf` to return an empty list if no attendance (good idea in general, as null object pattern is very often a life saver, and for collection, an empty collection is often semantically similar to null) 2) if you don't control that method, write a safe extension method which will return empty list in case of null, e.g.

List<AttendanceType> SafeAttendanceList(this AttendanceBALType bal, RollNumber rn)
{
    return bal.GetAttendanceListOf(rn) ?? new List<AttendanceType>();
}

Then call it as:

_AttendedDays = new AttendanceBAL()
    .SafeAttendanceListOf(q._RollNumber)
    .Where(date => date != null)

Problem

``` recordsList.ListOfRecords = new StudentRecordsBAL() .GetStudentsList() .Select(q => new StudentRecords() { _RollNumber = q._RollNumber, _Class = q._Class, _Name = q._Name, _Address = q._Address, _City = q._City, _State = q._State, _Subjects = q._Subject, _AttendedDays = new AttendanceBAL() .GetAttendanceListOf(q._RollNumber) .Where(date => date != null) .Select(date => new DateTime(date._Date.Year, date._Date.Month, date._Date.Day)) .Distinct() .ToList(), _AttendedSubjects = GetAttendedSubjects(q._RollNumber) }).ToList(); ``` The method, `GetAttendanceListOf(q._RollNumber)` in above code will return a list of records from the database or "null" if there are no records present for the passed "roll-no". A linq query will be terminated generating error "Value cannot be null". Is there a way to handle this error and make LINQ jump to next step?

Original source