ID标识字段值不会增加

Question

我有一个表单将id字段绑定为隐藏值。但在控制器中，id（键，自动标识增量）字段始终为0.以下是我的代码：

Model.cs

 public partial class A
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int id { get; set; }
    [StringLength(255)]
    [Display(Name = "Institution Name")]
    [Required]
    public string InstitutionName { get; set; }


    [Display(Name = "Public")]
    [DefaultValue(false)]
    public bool Category1 { get; set; }
    [Display(Name = "Private")]
    [DefaultValue(false)]


    [Display(Name = "Online")]
    [DefaultValue(false)]
    public bool Category3 { get; set; }
    [
    [Display(Name = "Active?")]
    [DefaultValue(false)]
    public bool active { get; set; }


    public A()
    {
        Category1 = false;
        Category2 = false;
        Category3 = false;
        active = true;

    }
}

控制器：

...
 [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "id,InstitutionName,Category1,Category2,Category3,active")] A A)
    {
        if (ModelState.IsValid)
        {

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

        return View(A);
    }
}

...

查看 - Create.cshtml：

@using (Html.BeginForm()) 
{
  @Html.AntiForgeryToken()

  <div class="form-horizontal">
      <h4>TransferSearch_revised</h4>
      <hr />
      @Html.HiddenFor(model=> model.id)
      @Html.ValidationSummary(true, "", new { @class = "text-danger" })
      <div class="form-group">
        @Html.LabelFor(model => model.InstitutionName, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.InstitutionName, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.InstitutionName, "", new { @class = "text-danger" })
        </div>
    </div>

...

id值为0或为空。我的代码出了什么问题？感谢。