asp.net MVC - code first外键允许我输入任何内容

   public int OrderId { get; set; }

   public string OrderName { get; set; }

   public int CustomerId { get; set; }

   [ForeignKey("CustomerId")]

   public Customer Customer { get; set; }

   public int CustomerId { get; set; }

   public string CustomerName { get; set; }

   public DbSet<Order> Orders { get; set; }

   public DbSet<Customer> Customers { get; set; }

   protected override void OnModelCreating(DbModelBuilder modelBuilder)

   {

       modelBuilder.Entity<Order>()

           .HasRequired(o => o.Customer)

           .WithMany()

           .HasForeignKey(o => o.CustomerId);

       base.OnModelCreating(modelBuilder);

   }

   if (ModelState.IsValid)

   {

       // 保存订单到数据库

       dbContext.Orders.Add(order);

       dbContext.SaveChanges();

       return RedirectToAction("Index");

   }

   // 验证失败，返回创建视图

   return View(order);