CODEWITHSUNDEEP
c#sql-serverlinq
Nazmul
Nazmul

Reputation: 143

Left outer join now working linq object reference not set to an instance of an object

I have two tables which i want to link via left outer join. Why the below query is returning me this error?

"linq query object reference not set to an instance of an object"

IEnumerable<RoadTrafficCount> roadTrafficCounts =
    _unitOfWork.RoadTrafficCountRepository
        .Get(i => i.ThanaID == thanaid && i.RoadID == roadid, includeProperties: "VehicleList, VehicleList.VehicleType");

IEnumerable<VehicleList> vehicleLists = _unitOfWork.VehicleListRepository.Get();

var q = (from pd in vehicleLists
         join od in roadTrafficCounts
         on pd.VehiID equals od.VehiID
         into t
         from rt in t.DefaultIfEmpty()
         orderby pd.VehiID
         select new
         {
             Id=(int?)rt.Id,
             ThanaId=(int?)rt.ThanaID,
             RoadID = (int?)rt.RoadID,
             pd.VehiID,
             pd.VehicleName,
             pd.VehiDescription,
             rt.CountHatDay,
             rt.CountNonHatDay
         }).ToList();

I have attached the table Design.How can i solve this ?

Table design picture

Update: I have tried Tim's approach using the conditional operator to avoid accesssing a property on a null reference. But i still get this error:

enter image description here

Upvotes: 1

Views: 801

Answers (1)

Tim Schmelter
Tim Schmelter

Reputation: 460098

rt will be null if the VehiID of RoadTrafficCount doesn't exist in VehicleListRepository. Then you get the exception on (int?)rt.Id, (int?)rt.RoadID and so on.

You can use the conditional operator to check if it's null:

... 
select new
{
    Id =            rt == null ? (int?)null : rt.Id,
    ThanaId =       rt == null ? (int?)null : rt.ThanaID,
    RoadID =        rt == null ? (int?)null : rt.RoadID,
    pd.VehiID,
    pd.VehicleName,
    pd.VehiDescription,
    rt.CountHatDay =     rt == null ? (int?)null : rt.CountHatDay,
    rt.CountNonHatDay =  rt == null ? (int?)null : rt.CountNonHatDay
})
....

Upvotes: 1

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