Ytukyg

I have the following entities set up.

public class Car

{

    public int Id { get; protected set; }

    public HashSet<Wheel> FrontWheels { get; set; };

    public HashSet<Wheel> RearWheels { get; set; };

}



public class Wheel

{

    public int Id { get; protected set; }

    //public Car Car { get; set; }

    public double Diameter { get; set; }

    public double Width { get; set; }

}

A Car has Wheels. It interacts with the fronts and rears very differently and therefore they are held in different collections. A wheel by itself is neither a front or a rear (it could be either), it is only through its association with the car that it is given a position on the car.

I can set this up in EF Core 2.1 using the following config:

    modelBuilder.Entity<Car>().HasMany(car => car.FrontWheels).WithOne();

    modelBuilder.Entity<Car>().HasMany(car => car.RearWheels).WithOne();

This creates a Wheel table with two nullable fk columns, CarIdFrontWheel & CarIdRearWheel. I understand why it creates two columns and why they're nullable (only 1 fk column will be populated for each Wheel row, and that column describes the position on the car). This schema describes the situation and I am happy with that.

Now the problem starts when I want to add back in the commented out inverse navigation property - so that I can navigate from a Wheel to it's connected Car. However I configure it, EF always wants to add another fk named CarId to the Wheel table to map back to a Car. I understand why it needs to do this - Otherwise I'm attempting to ask one property (Wheel.Car) to partake in two relationships. Both fks could point to a different Car id, etc.

However, what I am asking seems logically reasonable from an entity relationship point of view. If we were writing this data access manually, we could make the schema work without this unnecessary (somewhat de-normalized) 3rd foreign key.

• Is this possible to configure these entities using just the two
  (CarIdFrontWheel & CarIdRearWheel) foreign keys?


• Should I instead just accept the existence of the CarId foreign key?


• Or, are there some changes I can make to my model to help this situation?