Entity Framework objects being duplicated in the database

Question

I am working with Entity Framework (code first) for the first time and I have a little problem.

I have a class called Taxi & one called Driver

Taxi has a reference to the Driver, you can see both classed below

  public partial class Taxi
    {
        public Taxi()
        {
        }

        public int TaxiId { get; set; }
        public Driver Driver { get; set; }
        public string Make { get; set; }
        public string Model { get; set; }
        public Color Colour { get; set; }
        public string NumPlate { get; set; }
        public int MaxPassengers { get; set; }
}


    public partial class Driver
    {
        public Driver()
        {

        }

        public int DriverId { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Address { get; set; }
        public string HomePhone { get; set; }
        public string MobilePhone { get; set; }
        public DateTime JoinedFirm { get; set; }
}

And I am saving the changed Taxi like this:

 using (var db = new DataModel())
        {
            db.Configuration.ProxyCreationEnabled = false;

            db.Taxis
                .Where(x => x.TaxiId == CurrenltySelectedTaxi.TaxiId)
                .ToList()
                .ForEach(x =>
                {
                    x.Make = CurrenltySelectedTaxi.Make;
                    x.Model = CurrenltySelectedTaxi.Model;
                    x.NumPlate = CurrenltySelectedTaxi.NumPlate;
                    x.Colour = CurrenltySelectedTaxi.Colour;
                    x.MaxPassengers = CurrenltySelectedTaxi.MaxPassengers;
                    x.Driver = CurrenltySelectedTaxi.Driver;
                });

            db.SaveChanges();
        }

My problem is that the Driver gets duplicated the in database every time I save a taxi.

You can see the database here:

Can someone point me in the right direction, Thanks

EDIT: The drivers are in a combo box and are selected like this

private void cmbTaxiDriver_SelectedIndexChanged(object sender, EventArgs e)
{
    using (var db = new DataModel())
    {
        db.Configuration.ProxyCreationEnabled = false;
        Driver listSelected = (Driver) cmbTaxiDriver.SelectedItem;
        CurrenltySelectedTaxi.Driver = db.Drivers.Where(x => x.DriverId == listSelected.DriverId).ToArray()[0];
    }
}

And the combo box is populated like this:

        listDrivers.Items.AddRange(db.Drivers.ToArray());

Answer 1

The only thing that I can possibly find based on the content you have provided is that CurrenltySelectedTaxi.Driver is a detached or new driver. Be careful to ensure that the object pointed to by CurrenltySelectedTaxi.Driver is an attached driver record.

An option you can do to help determine the status of that record is to put a breakpoint on that line and then look at the DbEntry record status.

Answer 2

Your design doesn't create a relationship between Taxi and Driver that's going to translate to a database. Try something like this:

public partial class Taxi
    {
        public Taxi()
        {
        }
        public int TaxiId { get; set; }
        public int DriverId {get; set; }
        public virtual Driver Driver { get; set; }
        public string Make { get; set; }
        public string Model { get; set; }
        public Color Colour { get; set; }
        public string NumPlate { get; set; }
        public int MaxPassengers { get; set; }
}

You may also want to add the following to the Driver object:

public virtual IEnumerable<Taxi> Taxis { get; set; }

Answer 3

So it turns out my issue is because i followed the tutorial on MSDN that says to recreate your context EVERYTIME you use it. Although this 'may' be good practice, in this instance it caused the problem.

If I make one context for the entire class it works as expected/