实体框架关系问题

Question

我正在努力跟踪一个汽车零件是否已在当地总部和州总部之间进行了维修。我在Parts表中得到一个名为Car_Vin的附加字段。此外，当我抓住与汽车相关的记录时，我的记录集合总是回来为空。有人可以解释为什么会出现这两个问题吗？

public Car
{
    [Key]
    public string VIN{get;set;}
    //More fields go here
    public virtual ICollection<StateHQRecord> StateHQRecords{get;set;}
    public virtual ICollection<LocalHQRecord> LocalHQRecords{get;set;}
}

public Part{
{
    [Key]
    public string PartNumber{get;set;}
    //More fields go here
    public virtual ICollection<StateHQRecord> StateHQRecords{get;set;}
    public virtual ICollection<LocalHQRecord> LocalHQRecords{get;set;}
}

public class StateHQRecord
{
    public string VIN{get;set;}
    public string PartNumber{get;set;}
    public Car Car{get;set;}
    public Part Part{get;set;}
    public bool isRepaired{get;set;}
}

public class LocalHQRecord
{
    public string VIN{get;set;}
    public string PartNumber{get;set;}
    public Car Car{get;set;}
    public Part Part{get;set;}
    public bool isRepaired{get;set;}
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{

    modelBuilder.Entity<StateHQRecord>().HasKey(te => new {te.VIN, te.PartNumber});
        modelBuilder.Entity<StateHQRecord>().Map(m => m.ToTable("StateHQRecords"));
        modelBuilder.Entity<LocalHQRecord>().HasKey(te => new {te.VIN, te.PartNumber});
        modelBuilder.Entity<LocalHQRecord>().Map(m => m.ToTable("LocalHQRecords")); 

    modelBuilder.Entity<Car>().HasKey(a => a.VIN);
        modelBuilder.Entity<Car>().
                HasMany(a => a.StateHQRecords).
                WithRequired(te => te.Car).
                HasForeignKey(te => te.VIN);
    modelBuilder.Entity<Car>().
                HasMany(a => a.LocalHQRecords).
                WithRequired(te => te.Car).
                HasForeignKey(te => te.VIN);

    modelBuilder.Entity<Part>().HasKey(a => a.PartNumber);
        modelBuilder.Entity<Part>().
                HasMany(a => a.StateHQRecords).
                WithRequired(te => te.Part).
                HasForeignKey(te => te.PartNumber);
    modelBuilder.Entity<Part>().
                HasMany(a => a.LocalHQRecords).
                WithRequired(te => te.Part).
                HasForeignKey(te => te.PartNumber);

}


public void AddCarToLocalHQ(Car car,Part part)
{
    var currentCarEntityState=EntityState.Modified;
    var currentPartEntityState=EntityState.Modified;
    var currentCar=context.Cars.FirstOrDefault(c=>c.VIN==car.VIN);
    var currentPart=context.Parts.FirstOrDefault(p=>p.PartNumber==part.PartNumber);

    if(currentCar==null)
    {
        currentCar=car;
        currentCarEntityState=EntityState.Added;
    }
    if(currentPart==null)
    {
        currentPart=part;
        currentPartEntityState=EntityState.Added;
    }

    var currentRecord=context.LocalHQRecords.FirstOrDefault(r=>r.VIN==currentCar.VIN && r.PartNumber==currentPart.PartNumber);
    if(currentRecord!=null)
    {
        throw new DuplicateRecordException();
    }

    currentRecord=new LocalHQRecord{Car=currentCar,Part=currentPart};
    currentCar.LocalHQRecords.Add(currentRecord);
    currentPart.LocalHQRecords.Add(currentRecord);
    context.Entry(currentCar).State=currentCarEntityState;
    context.Entry(currentPart).State=currentPartEntityState;
    context.SaveChanges();
}