EF Foreign Key using Fluent API

Question

Here are my models. I have one to one mapping for Vehicle and Driver. I will have the vehicle created first and then map the driver to the vehicle.

public class Driver
{
    public int Id { get; set; }
    public String Name { get; set; }
    public int VehicleId { get; set; }
    public virtual Vehicle Vehicle  { get; set; }
}

public class Vehicle
{  
    public int Id { get; set; }
    public String Name { get; set; }

    public virtual Driver Driver { get; set; }

    public int VehicleGroupId { get; set; }
    public virtual VehicleGroup Vehicles { get; set; }
}

I want to use VehicleId property in Driver class to keep id of vehicle the driver is driving.

I've written the following Fluent API code:

modelBuilder.Entity<Vehicle>()
            .HasRequired(d => d.Driver)
            .WithRequiredPrincipal();

But it creates a new column in Drivers table - Vehicle_VehicleId and maps it to the VehicleId on Vehicle table. I want the VehicleId of Driver table to map.

Also, i'm brand new to EF and Fluent API. I find it extremely confusing choosing between WithRequiredDependent and WithRequiredPrincipal. Would be glad if you can describe it in simple words. Thanks.

Answer 1

This line:

public int VehicleId { get; set; }

is telling EF, through code-conventions, that you want a foreign key in Driver pointing to Vehicle.

The following is telling EF that you want a 1:1 relationship from Driver to Vehicle:

public virtual Vehicle Vehicle { get; set; }

You should remove both and stick with your Fluent API configuration.

Regarding WithRequiredPrincipal vs. WithRequiredDependent:

You are specifying a compulsory relationship between Vehicle and Driver, with navigation from Vehicleto Driver, thus: Vehicle 1 --> 1 Driver

(Vehicle is the principal and Driver the dependent, since the navigation property is located in Vehicleand pointing to Driver .)

modelBuilder.Entity<Vehicle>()
            .HasRequired(d => d.Driver)
            .WithRequiredDependent();

You are specifying a compulsory relationship between Vehicle and Driver, with navigation from Driver to Vehicle, thus: Vehicle 1 <-- 1 Driver

(Vehicle is the dependent and Driver the principal, since the navigation property is located in Driver pointing to Vehicle.)

These two are analogous:

modelBuilder.Entity<Vehicle>()
            .HasRequired(v => v.Driver)
            .WithRequiredPrincipal();

modelBuilder.Entity<Driver>()
            .HasRequired(d => d.Vehicle)
            .WithRequiredDependent();