系统数据SqlClient。SqlException:“无法删除数据库。”。如何解决?

我在我的类模型用户中添加了一个属性“password”。在我看来 Register.cshtml 现在

 <form action="~/Users/SaveRegister" method="post">

            @Html.ValidationSummary(true)

            @Html.AntiForgeryToken()
            <div class="editor-label">
                @Html.LabelFor(model => model.user_name)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.user_name)
                @Html.ValidationMessageFor(model => model.user_name)
            </div>

            <div class="editor-label">
                @Html.LabelFor(model => model.password)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.password)
                @Html.ValidationMessageFor(model => model.password)
            </div>
            <p>
                <input type="submit" value="Register" />
            </p>
    </form>

但我的控制器出现了一个例外 db.Users.Add(User); 当我按下 Register .

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult SaveRegister(Airlineapp.Models.User User, HttpPostedFileBase file)
{

    db.Users.Add(User);
    db.SaveChanges();
    return RedirectToAction("Index");
}