出现错误 可选参数必须是引用类型、可空类型或声明为可选参数

Question

将数据更新到数据库后出现错误

参数字典包含方法“System.Web.Mvc.ActionResult UpdateChain(Int32, HCIBE.Models.chain)”的不可空类型“System.Int32”的参数“id”的空条目'HCIBE.Controllers.ChainsController'。可选参数必须是引用类型、可空类型或声明为可选参数。

这是我的控制器

    [HttpGet]
    public ActionResult UpdateChain(int? id)
    {
        chain objchain = db.chains.Find(id);
        if (objchain == null)
        {
            return HttpNotFound();
        }
        return View(objchain);
    }

    [HttpPost]
    public ActionResult UpdateChain(int id, [Bind(Include = "name,code,username,password,updated_by,updated_on")] chain chain)
    {
        chain _objchain = db.chains.Find(id);
        try
        {
        if(ModelState.IsValid)
        {
            _objchain.code = chain.code;
            _objchain.name = chain.name;
            _objchain.username = chain.username;
            _objchain.password = chain.password;
            _objchain.updated_by = Convert.ToInt32("1");
            _objchain.updated_on = DateTime.Now;

            db.Entry(_objchain).State = EntityState.Modified;
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        }
        catch (Exception Ex)
        {
            ModelState.AddModelError("", "Unable to update data");
        }
        return View(_objchain);
    }

查看

@using (@Html.BeginForm("UpdateChain", "Chains", FormMethod.Post))
{

<div class="form-horizontal">
    <hr />
    <div class="form-group">
        <label class="col-sm-2 control-label">
            Select Chain
        </label>
        <div class="col-md-3">
            @Html.DropDownList("ddlchainname", (SelectList)ViewData["chain_name"],"Select Chain", new { onchange = "Action(this.value);", @class = "form-control" })
        </div>
        <label class="control-label">
            or @Html.ActionLink("Add New", "Create")

        </label>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">
            Chain Name
        </label>
        <div class="col-md-3">
            @Html.TextBox("ChainName", null, new { @class = "form-control" })
        </div>
        <label class="col-sm-2 control-label">
            Username
        </label>
        <div class="col-md-3">
            @Html.TextBox("username", null, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        <label class="col-sm-2 control-label">
            Chain Code
        </label>
        <div class="col-md-3">
            @Html.TextBox("ChainCode", null, new { @class = "form-control" })
        </div>
        <label class="col-sm-2 control-label">
            Password
        </label>
        <div class="col-md-3">
            @Html.Password("password", null, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Update" onclick="UpdateChain()" class="btn btn-default" />
        </div>
    </div>
</div>
}

<script type="text/javascript">
    function UpdateChain(){
        var _vddlChainID = $("#ddlchainname").val();
        alert("Your Selected ID = " + _vddlChainID);
        $.ajax({
            url: '@Url.Action("UpdateChain", "Chains")',
            type: "POST",
            data: { "id": _vddlChainID }
        });
    }
</script>

通过下拉选择我填写所有文本框，当我提交表单时我得到错误。

路由

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );
    }

型号

public partial class chain
{
    public chain()
    {
        this.templates = new HashSet<template>();
        this.hotels = new HashSet<hotel>();
    }

    public long chain_id { get; set; }
    public string name { get; set; }
    public string code { get; set; }
    public string username { get; set; }
    public string password { get; set; }
    public long created_by { get; set; }
    public System.DateTime created_on { get; set; }
    public Nullable<long> updated_by { get; set; }
    public Nullable<System.DateTime> updated_on { get; set; }

    public virtual ICollection<template> templates { get; set; }
    public virtual ICollection<hotel> hotels { get; set; }
}

Answer 1

您正在传递chain 的object，但您没有在任何地方添加id 的值。需要设置value of id，并添加到chain object中。

Answer 2

当您提交表单时您的 id 为空，这就是您收到此错误的原因。

要么像在get方法中那样指定id参数为空，要么

将 id 存储在隐藏字段中，以便像这样与模型一起自动传递它

@HTML.HiddenFor(Model.id)

或手动传递

@HTML.Hidden("id",id)