CODEWITHSUNDEEP
c#asp.netentity-frameworkpropertieslazy-loading
Mara
Mara

Reputation: 118

ASP.NET Entity Framework property not loaded while ID filled

This is something that worked up to now and now it just, stopped working (I know, weird, there's probably some silly mistake..)

I have a TripsVM, which contains a list of trips. I load these in my service, returning a List<>.

The problem occurs when I iterate over the trips collection and try to get trip.TripCategory.Name, as the TripCategory is empty, even though TripCategoryID has a value.

This all happens at the backend, I load the trips and then try to iterate over them, they are not being send from the page.

I could probably just load the trip by trip itself, but it used to work and this bug just came up after months of usage.

Any suggestions of where to look for bugs would be really appreciated.

Thanks

Error:

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

Where error occurs:

foreach (Trip trip in tripsVM.TripsList) {
    var a = trip.TripCategory.Name;

TripsVM:

    private List<Trip> _TripsList;

    public List<Trip> TripsList
    {
        get
        {
            if (_TripsList == null)
            {
                _TripsList = TripsService.GetTrips();

                if (_TripsList == null)
                    _TripsList = new List<Trip>();
            }

            return _TripsList;
        }
        set { _TripsList = value; }
    }

Service:

public static List<Trip> GetTrips()
{ 
     return DB.Trips.Where(...).OrderBy(...).ToList(); 
}

Trip class: 

public partial class Trip
{
    public int TripID { get; set; }
    public int TripCategoryID { get; set; }
    ....
    public virtual TripCategory TripCategory { get; set; }
}

Upvotes: 1

Views: 426

Answers (2)

knightRider
knightRider

Reputation: 153

I think your code looks fine but you should add some if statements to avoid null exception, because you are returning something with where clause, so you might end up with empty query result and empty list, and in that list you are trying to reach an element of a list object:

if(tripsVM.TripsList != null){
     foreach (Trip trip in tripsVM.TripsList) {
     var a = trip.TripCategory.Name;
     }
}

else
{
   // handle empty list
}


 private List<Trip> _TripsList;

        public List<Trip> TripsList
        {
            get
            {
            _TripsList = new List<Trip>();
            if(TripsService.GetTrips() != null)
              {
             _TripsList.add(TripsService.GetTrips());
              }
                return _TripsList;
            }
            set { _TripsList = value; }
        }

Upvotes: 0

YuriyP
YuriyP

Reputation: 4478

Its looks like your DB context disposed before foreach code or LazyLoadingEnabled set to false in context.

In Service add using

using System.Data.Entity;

And modify loading method

public static List<Trip> GetTrips()
{ return DB.Trips.Where(...).Include(t=>t.TripCategory).OrderBy(...).ToList(); }

Upvotes: 2

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