实体框架一对多与每个层次的每个子类创建一个外键列 [英] Entity Framework one-to-many with table-per-hierarchy creates one foreign key column per subclass

问题描述

我有一个 Garage ，其中包含 Cars 和摩托车。汽车和摩托车是车辆。这里是：

I have a Garage which contains Cars and Motorcycles. Cars and motorcycles are Vehicles. Here they are:

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...
}

为什么汽车和摩托车每个都有一个GarageId和Garage属性？如果我把这些属性推到车辆超类，EF会抱怨告诉我导航属性必须位于具体的类中。

Why do Car and Motorcycle each have a GarageId and Garage property? If I push those properties up to the Vehicle superclass, EF complains and tells me navigation properties must reside in concrete classes.

继续，这里是我的DbContext：

Moving on, here's my 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>();
    }
}

这是一个简短的程序来玩我的玩具：

And here's a short program to play with my toys:

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车辆表：

The program runs, and produces the following Vehicles table:

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

汽车和摩托车都有自己的GarageId和Garage属性，似乎每个子类都在创建自己的外挂车库。如何可以告诉EF（如果可能，通过流畅的api）Car.Garage和Motorcycle.Garage是一样的，应该使用相同的列？

With both Car and Motorcycle having their own GarageId and Garage properties, it seems that each subclass is creating its own foreign key to garage. How do I tell EF (via the fluent api, if possible) that Car.Garage and the Motorcycle.Garage are the same thing, and should use the same column?

这是我想要的车辆表：

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

推荐答案

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

Use attribute [Column("GarageId")] on GarageId property on both car and motorcycle class.

这篇关于实体框架一对多与每个层次的每个子类创建一个外键列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！