Question

I have written a 3 layer web site which has singleton repository for accessing database. My repositories use dataset for connecting to and query from database.
I want to test the site using Visual Studio 2010 Test project but when I create TableAdapter of dataset in repository I got following error in test application:

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

the code work correctly when I use repository from the inside of site but in test application I got that error.
one of my repositories which I got that error is follow:

public sealed class VehicleRepository
{
    private readonly int gateCode;
    private readonly VehicleTableAdapter vehicleSet;
    private readonly VehicleTypeTableAdapter vehicleTypeSet;
    private static VehicleRepository instance;

    private VehicleRepository()
    {
        var configureTable = new ConfigurationTableAdapter();
--->>>      var configuration = configureTable.GetData().ToList();
            if (configuration.Count == 0)
                throw new UserInterfaceException("some message");
            if (configuration.Count != 1)
                throw new UserInterfaceException("some message");
            gateCode = configuration[0].GateCode;
            vehicleSet=new VehicleTableAdapter();
            vehicleTypeSet=new VehicleTypeTableAdapter();
        }

    public static VehicleRepository GetInstance()
    {
        return instance ?? (instance = new VehicleRepository());
    }

    public Vehicle GetVehicleByPlaque(string plaque)
    {
        .....
    }

    private static Vehicle ConvertVehicleRowToVehicle(TransportCo.VehicleRow vehicleRow,TransportCo.VehicleTypeRow vehicleTypeRow)
    {
        ....
    }

    public void SaveOrUpdate(Vehicle vehicle)
    {
        ...
    }

    private static void UpdateVehicle(Vehicle vehicle)
    {
       ...
    }
}

I got the error in the —>>> line.
does anyone know the problem?

Answer 1

I suspect that if you break that line into two steps and look at what GetData returns, you’ll see it is null.