小编ili*_*rvg的帖子

我试图在我的下拉列表中允许空值,在我的数据库表中,我为该特定字段设置了允许空值,但是当我运行代码时,我得到错误,说"可以为空的对象必须有值",我想问题可能出在ModelState中.

调节器

[HttpPost]
    public ActionResult Edit(Student student)
    {
        if (ModelState.IsValid)
        {
            db.Entry(student).State = EntityState.Modified;
            db.SaveChanges();
            Loan w = new Loan()
            {
                StudentID = student.StudentID,
                ISBN = student.ISBN.Value,
            };
            db.Loans.Add(w);
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        ViewBag.ISBN1 = new SelectList(db.Books, "ISBN", "Titulli", student.ISBN);
        return View(student);
    }