C#到F# - EF代码优先

Question

我和Dealer谁之间有一对多的关系Cars.

我正在尝试将用于EF的C#代码转换为F#...问题只是在我的F#代码中它可以很好地获得经销商,但它不会为该经销商...它只是返回null,但在它的C#版本有效吗？

我的代码:

C#版本

public class Dealer
{
    public int ID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Car> Cars { get; set; }

    public Dealer()
    {
        Cars = new List<Car>();
    }
}
public class Car
{
    public int ID { get; set; }
    public string CarName { get; set; }
    public Dealer Dealer { get; set; }
    public int DealerId { get; set; }

    public Car()
    {
        Dealer = new Dealer();
    }
}
public class MyContext : DbContext
{
    public DbSet<Dealer> Dealers { get; set; }
    public DbSet<Car> Cars { get; set; }
    public MyContext()
    {
        Database.Connection.ConnectionString = "server=some;database=dbname;user id=uid;password=pwd";
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Dealer>()
            .HasMany(x => x.Cars)
            .WithRequired(x => x.Dealer)
            .HasForeignKey(x => x.DealerId);

        modelBuilder.Entity<Car>()
            .HasRequired(x => x.Dealer)
            .WithMany()
            .HasForeignKey(x => x.DealerId);

        modelBuilder.Entity<Dealer>().ToTable("Dealers");
        modelBuilder.Entity<Car>().ToTable("Cars");
    }
}

...查询经销商及其汽车的Program.cs:

static void Main(string[] args)
{
    var ctx = new MyContext();
    foreach (var s in ctx.Dealers.FirstOrDefault(x => x.ID == 1).Cars)
    {
        Console.WriteLine(s.CarName);
    }

    Console.Read();
}

F#版本

type Dealer() =
    let mutable id = 0
    let mutable name = ""
    let mutable cars = List<Car>() :> ICollection<Car>
    member x.ID with get() = id and set v = id <- v
    member x.Name with get() = name and set v = name <- v
    abstract member Cars : ICollection<Car> with get, set
    override x.Cars with get() = cars and set v = cars <- v
and Car() =
    let mutable id = 0
    let mutable carName = ""
    let mutable dealer = Dealer()
    let mutable dealerId = 0
    member x.ID with get() = id and set v = id <- v
    member x.CarName with get() = carName and set v = carName <- v
    member x.Dealer with get() = dealer and set v = dealer <- v
    member x.DealerId with get() = dealerId and set v = dealerId <- v


type MyContext() =
    inherit DbContext("server=some;database=dbname;user id=uid;password=pwd")

    [<DefaultValue>] val mutable dealers : DbSet<Dealer>
    member x.Dealers with get() = x.dealers and set v = x.dealers <- v

    [<DefaultValue>] val mutable cars : DbSet<Car>
    member x.Cars with get() = x.cars and set v = x.cars <- v

    override x.OnModelCreating(modelBuilder:DbModelBuilder) =
        modelBuilder.Entity<Dealer>()
            .HasMany(ToLinq(<@ fun ka -> ka.Cars @>))
            .WithRequired(ToLinq(<@ fun sk -> sk.Dealer @>))
            .HasForeignKey(ToLinq(<@ fun fg -> fg.DealerId @>)) |> ignore

        modelBuilder.Entity<Car>()
            .HasRequired(ToLinq(<@ fun ak -> ak.Dealer @>))
            .WithMany()
            .HasForeignKey(ToLinq(<@ fun ka -> ka.DealerId @>)) |> ignore

        modelBuilder.Entity<Dealer>().ToTable("Dealers")
        modelBuilder.Entity<Car>().ToTable("Cars")

...功能ToLinq:

let ToLinq (exp : Expr<'a -> 'b>) = 
    let linq = exp.ToLinqExpression() 
    let call = linq :?> MethodCallExpression
    let lambda = call.Arguments.[0] :?> LambdaExpression 
    Expression.Lambda<Func<'a, 'b>>(lambda.Body, lambda.Parameters)

......以及将获得经销商和他的汽车的Program.fs:

let ctx = new MyContext()
let joe = ctx.Dealers.Find(1)
joe.Cars |> Seq.iter(fun x -> printfn "%s" x.CarName)
printfn "DONE"

任何帮助表示赞赏!

Answer 1

更改

let mutable cars = List<Car>() :> ICollection<Car>

至

let mutable cars = Unchecked.defaultof<ICollection<Car>>

和

let mutable dealer = Dealer()   

至

let mutable dealer = Unchecked.defaultof<Dealer>