Getting a NullReference exception in for each loop

Question

As I iterate over my loop I am getting an when the iteration gets to OrderNo

System.NullReferenceException: Object reference not set to an instance of an object.

Code:

[HttpGet]
[Authorize]
public async Task<IActionResult> GetWorkSpaceNotifications()
{
   WorkSpaceViewModel ReqWkspace = new WorkSpaceViewModel();

   var reqWorkSpace = _context.Requisition.OrderByDescending(x => x.RequisitionId).ToList();
          
   foreach (var c in reqWorkSpace)
   {
       ReqWkspace.departmentName = _context.Department
                                           .Where(d => d.DepartmentId == c.DepartmentId)
                                           .FirstOrDefault()
                                           .DepartmentName;

       if (c.RequisitionTypeId != null)
       {
           ReqWkspace.requisitionType = _context.RequisitionType
                                                .Where(d => d.RequisitionTypeId == c.RequisitionTypeId)
                                                .FirstOrDefault()
                                                .Description;
       }
            
       ReqWkspace.ReqWorkSpace.RequisitionNo = c.OrderNo;
       ReqWkspace.ReqWorkSpace.QueriesEmail = c.QueriesEmail;
       ReqWkspace.ReqWorkSpace.DateCreated = c.DateCreated;
       ReqWkspace.ReqWorkSpace.Total = c.Total;
       ReqWkspace.Description = c.RequisitionTitle +""+ ReqWkspace.departmentName;
   }

   await Task.Run(() =>
            {
            });

   return View(reqWorkSpace);
}

Do you initialize the ReqWorkSpace property in the WorkSpaceViewModel constructor? — Osama, Oct 10 '22 at 15:44

score 1 · Accepted Answer · answered Oct 10 '22 at 16:38

If this line:

ReqWkspace.ReqWorkSpace.RequisitionNo = c.OrderNo

Is throwing that exception, then there are four possible causes:

ReqWkspace.ReqWorkSpace is null (seems most likely)
c is null (seems unlikely given the query that creates c)
The getter for either OrderNo or ReqWorkSpace has code that throws that exception (seems very unlikely)
The setter for RequisitionNo has code that throws that exception (seems very unlikely).

There's no way that we can tell which is the problem. I would run it in the debugger, and either break on exception or just view the properties in the first iteration to see if something is not getting initialized.

score 0 · Answer 2 · answered Oct 10 '22 at 15:59

You should handle these points properlly:

ReqWkspace.departmentName = _context.RequisitionType
                                            .Where(d => d.RequisitionTypeId == c.RequisitionTypeId)
                                            .FirstOrDefault()
                                            .DepartmentName;

If the result of this is null you will get null reference exception so you should defense in that for example:

    var requisitionType = _context.RequisitionType
                                                    .Where(d => d.RequisitionTypeId == c.RequisitionTypeId)
                                                    .FirstOrDefault();
    
ReqWkspace.requisitionType = requisitionType == null ? string.Empty : requisitionType.DepartmentName;

or simply you can do this:

ReqWkspace.requisitionType = _context.RequisitionType
                                                .Where(d => d.RequisitionTypeId == c.RequisitionTypeId)
                                                .FirstOrDefault()?
                                                .DepartmentName;

Same in the description.

Make sure that you initialized the ReqWorkSpace inside the WorkSpaceViewModel constructor.

Getting a NullReference exception in for each loop

2 Answers2