c# - Entity Framework 一对多，每个层次结构一个表，为每个子类创建一个外键列

Question

我有一个 Garage，其中包含 Cars 和 Motorcycles。汽车和摩托车是 Vehicles。他们在这里:

public class Garage
{
    public int Id { get; set; }
    public virtual List<Car> Cars { get; set; }
    public virtual List<Motorcycle> Motorcycles { get; set; }

    public Garage()
    {
        Cars = new List<Car>();
        Motorcycles = new List<Motorcycle>();
    }
}

public abstract class Vehicle
{
    public int Id { get; set; }
    public string Make { get; set; }
    public string Model { get; set; }
}

public class Car : Vehicle
{
    public int GarageId { get; set; }
    public virtual Garage Garage { get; set; }
    // some more properties here...
}

public class Motorcycle : Vehicle
{
    public int GarageId { get; set; }
    public virtual Garage Garage { get; set; }
    // some more properties here...
}

为什么 Car 和 Motorcycle 都有 GarageId 和 Garage 属性？如果我将这些属性推送到 Vehicle 父类(super class)，EF 会提示并告诉我导航属性必须驻留在具体类中。

继续，这是我的 DbContext:

public class DataContext : DbContext
{
    public DbSet<Garage> Garages { get; set; }
    public DbSet<Vehicle> Vehicles { get; set; }
    public DbSet<Car> Cars { get; set; }
    public DbSet<Motorcycle> Motorcycles { get; set; }

    public DataContext()
        : base("GarageExample")
    {

    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
        modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
    }
}

这是一个玩我的玩具的小程序:

class Program
{
    static void Main(string[] args)
    {
        Database.SetInitializer<DataContext>(new DropCreateDatabaseAlways<DataContext>());

        using (var db = new DataContext())
        {
            var car1 = new Car { Make = "Subaru", Model = "Legacy" };
            var car2 = new Car { Make = "Porche", Model = "911" };

            var bike1 = new Motorcycle { Make = "Suzuki", Model = "GS500" };
            var bike2 = new Motorcycle { Make = "Kawasaki", Model = "Ninja" };

            var garage = new Garage();

            garage.Cars.Add(car1);
            garage.Cars.Add(car2);
            garage.Motorcycles.Add(bike1);
            garage.Motorcycles.Add(bike2);

            db.Garages.Add(garage);

            db.SaveChanges();
        }
    }
}

程序运行，并生成以下Vehicles 表:

Id Make     Model  GarageId GarageId1 Discriminator
1  Subaru   Legacy 1        null      Car
2  Porche   911    1        null      Car
3  Suzuki   GS500  null     1         Motorcycle
4  Kawasaki Ninja  null     1         Motorcycle

由于 Car 和 Motorcycle 都有自己的 GarageId 和 Garage 属性，似乎每个子类都在创建自己的车库外键。我如何告诉 EF(如果可能，通过 Fluent API)Car.Garage 和 Motorcycle.Garage 是同一个东西，并且应该使用相同的列？

这当然是我想要的Vehicles表:

Id Make     Model  GarageId Discriminator
1  Subaru   Legacy 1        Car
2  Porche   911    1        Car
3  Suzuki   GS500  1        Motorcycle
4  Kawasaki Ninja  1        Motorcycle

Answer 1

在汽车和摩托车类的 GarageId 属性上使用属性 [Column("GarageId")]。