Question

I need to query one object with its related objects, I am using the unit of work pattern and repository pattern.

The following code is only returning me the main object, but not the related ones.

public List<EcoBonusRequest> GetAllRequestsWaitForPayment()
            {
                return _context.EcoBonusRequests.Where(p => p.CurrentStatus == RequestStatus.WaitingForPayment).Include("Dealer").Include("Vehicle").ToList();
            }

So I am getting a null reference exception when I try use the Dealer and the Vehicle of that object on my page

public void Databind(EcoBonusRequest ecoBonusRequest)
        {
            if (ecoBonusRequest != null)
            {
                LblRegistrationNumberValue.Text = ecoBonusRequest.Dealer.Nuteres; ---> Exception here

Repository

public class UnitOfWork : IDisposable
    {
        #region Variables
            private readonly AskAndTrackContext _context = new AskAndTrackContext();
            private RequestBaseRepository _requestBaseRepository;
            private EcoBonusRequestRepository _ecobonusworkflowRepository;

 public RequestBaseRepository RequestBaseRepository
            {
                get
                {
                    return _requestBaseRepository ??
                            (_requestBaseRepository = new RequestBaseRepository(_context));
                }
            }

            public EcoBonusRequestRepository EcoBonusRequestRepository
            {
                get
                {
                    return _ecobonusworkflowRepository ??
                            (_ecobonusworkflowRepository = new EcoBonusRequestRepository(_context));
                }
            }

Update1: Entities

public class RequestBase
    {
        public int RequestBaseId { get; set; }
        public string CurrentStatus { get; set; }
        public string RequestNumber { get; set; }

        [Column(TypeName = "Date")]
        public DateTime RequestDate { get; set; }
        public bool IsOnHold { get; set; }

        public virtual Dealer Dealer { get; set; }
        public virtual Requester Requester { get; set; }
        public virtual Vehicle Vehicle { get; set; }

        public virtual ICollection<Attachment> Attachments { get; set; }
        public virtual ICollection<WorkflowHistory> WorkflowHistories { get; set; }


 public class EcoBonusRequest : RequestBase
    {
        public string BrandReturnedVehicle { get; set; }

        public string TypeReturnedVehicle { get; set; }

        public string ChassisReturnedVehicle { get; set; }

DbContext

public class AskAndTrackContext : DbContext
    {
        public AskAndTrackContext() : base("AskAndTrack")
        {
            //It doesnt create the database.
            //Database.SetInitializer<AskAndTrackContext>(null);
            //Database.SetInitializer<AskAndTrackContext>(new AskAndTrackDevInitializer());
        }

        public DbSet<RequestBase> RequestBases { get; set; }
        public DbSet<EcoBonusRequest> EcoBonusRequests { get; set; }

Answer 1

Well, Include means that the referenced entity will be eager loaded.

But if the referenced entity is nullable (and null in your query), query won’t be able to retrieve a non existing referenced entity.

So if ecoBonusRequest.Dealer == null… You will get a NRE.

EDIT : could you try to test this way ?

public List<EcoBonusRequest> GetAllRequestsWaitForPayment()
            {
                var query = _context.EcoBonusRequests.Where(p => p.CurrentStatus == RequestStatus.WaitingForPayment).Include("Dealer").Include("Vehicle");
                var dealerExists = query.All(m => m.Dealer != null);
                return query.ToList();
            }

EDIT 2:

Maybe a problem of inheritance and Include
Can you try

return _context.RequestBase
               .Where(p => p.CurrentStatus == RequestStatus.WaitingForPayment)
               .Include("Dealer")
               .Include("Vehicle")
               .OfType<EcoBonusRequests>()
               .ToList();