【发布时间】：2021-08-25 12:38:15
【问题描述】：
当我尝试添加评论时，我得到了返回。我真的不明白为什么我从要创建票证的地方创建错误？
这是我的错误来自的控制器，它指向obj.Ticket.Ticket_Id == 0
public IActionResult Create(TicketVM obj)
{
if (obj.Ticket.Ticket_Id == 0)
{
_db.Tickets.Add(obj.Ticket);
}
else
{
_db.Tickets.Update(obj.Ticket);
}
}
这是我收到的消息：
System.NullReferenceException: '对象引用未设置为对象的实例。'
WebApplication20.Models.TicketVM.Ticket.get 返回 null。
我尝试创建一个应用程序，我可以在其中创建一个项目对象，然后您应该能够为其创建票证，并且在我的票证中，我应该能够为特定票证制作 cmets。为了能够做到这一点，我在项目 --> 票证之间创建了一对多关系，然后在票证之间创建了一对多关系 --> 评论。
这就是我的票证控制器，我可以在其中创建更新和删除票证：
[Authorize]
public class TicketController : Controller
{
private readonly ApplicationDbContext _db;
public TicketController(ApplicationDbContext db)
{
_db = db;
}
public IActionResult Index()
{
IEnumerable<Ticket> objList = _db.Tickets;
foreach (var obj in objList)
{
obj.Project = _db.Projects.FirstOrDefault(u => u.Project_Id == obj.Project_Id);
}
return View(objList);
}
/**This is the view i want to create my operation on**/
public IActionResult Info(int id)
{
CommentVM t = new CommentVM();
t.Ticket = _db.Tickets.FirstOrDefault(t => t.Ticket_Id == id);
t.Comments = _db.Commenents.Where(f => f.Ticket_Id == id);
return View(t);
}
// Create
public IActionResult Create(int? id)
{
TicketVM obj = new TicketVM();
obj.ProjectList = _db.Projects.Select(i => new SelectListItem
{
Text = i.Name,
Value = i.Project_Id.ToString()
});
if (id == null)
{
return View(obj);
}
// Status List
#region
List<SelectListItem> statusList = new List<SelectListItem>();
statusList.Add(new SelectListItem()
{
Value = "Open",
Text = "Open"
});
statusList.Add(new SelectListItem()
{
Value = "Closed",
Text = "Closed"
});
#endregion
// Status List End
if (obj == null)
{
return NotFound();
}
obj.Ticket = _db.Tickets.FirstOrDefault(u => u.Ticket_Id == id);
obj.StatusList = statusList;
return View(obj);
}
/**This is the controller where i get my error from:**/
// POST Create/Update
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Create(TicketVM obj)
{
if (obj.Ticket.Ticket_Id == 0)
{
_db.Tickets.Add(obj.Ticket);
}
else
{
_db.Tickets.Update(obj.Ticket);
}
_db.SaveChanges();
return RedirectToAction(nameof(Index));
}
// Delete
public IActionResult Delete(int? id)
{
var dbObj = _db.Tickets.FirstOrDefault(u => u.Ticket_Id == id);
_db.Tickets.Remove(dbObj);
_db.SaveChanges();
return RedirectToAction("Index");
}
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Comments(CommentVM obj)
{
if(ModelState.IsValid)
{
_db.Commenents.Add(obj.Comment);
_db.SaveChanges();
return RedirectToAction(nameof(Index));
}
return View();
}
}
在底部我创建了一个注释控制器，我希望能够将 cmets 添加到数据库中。当我尝试从属于 Ticket 中的 InfoController 的视图中发表评论时，我收到一条警报，提示我的 TicketController 中的 Create / POST 中存在错误，其中显示“对象引用未设置为一个东西。'我完全不明白为什么我从 Creaste / POST 票证中收到错误消息？
这就是我的信息视图的样子
@model WebApplication20.ViewModel.CommentVM
@{
Layout = "_Dashboard";
var title = "About Ticket";
}
<html>
<body id="page-top">
<div class="card mx-auto" style="width: 18rem;">
<div class="card-header">
<h4><strong>Ticket Status</strong></h4> Created @Model.Ticket.TicketCreated
</div>
<ul class="list-group list-group-flush">
<li class="list-group-item"><strong>Name:</strong>@Model.Ticket.TicketName </li>
<li class="list-group-item"><strong>Descripton: @Model.Ticket.TicketDescription</strong></li>
<li class="list-group-item"><strong>Priority:</strong> @Model.Ticket.TicketPriority</li>
<li class="list-group-item"><strong>Type:</strong> @Model.Ticket.TicketType</li>
<li class="list-group-item"><strong>Status:</strong> @Model.Ticket.TicketStatus</li>
</ul>
</div>
<div class="card shadow mx-auto m-3" style="width: 42rem;">
<div class="card-header">
<h4><strong>Comments</strong></h4>
</div>
<div class="row">
<div class="col-md-4 p-4">
<form asp-action="Comments">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
<label asp-for="Message" class="control-label"></label>
<input asp-for="Message" class="form-control" />
<span asp-validation-for="Message" class="text-danger"></span>
</div>
<div class="form-group">
<input type="submit" value="Submit" class="btn btn-primary" />
</div>
</form>
</div>
</div>
@*TABLE*@
<div class="row">
<!-- Area Chart -->
<div class="col-xl-8 col-lg-7">
<div class="card shadow mb-4">
<!-- Card Header - Dropdown -->
<div class="card-header py-3 d-flex flex-row align-items-center justify-content-between">
<h6 class="m-0 font-weight-bold text-primary">Current Comments</h6>
</div>
@if (Model.Comments.Count() > 0)
{
<table class="table table-bordered table-striped" style="width:100%">
<thead>
<tr>
<th>
Message
</th>
<th>
Submitter
</th>
<th>
Created
</th>
</tr>
</thead>
<tbody>
@foreach (var comment in Model.Comments)
{
<tr>
<td width="10%">
@comment.Message
</td>
<td width="10%">
</td>
<td width="10%">
@comment.Created
</td>
</tr>
}
</tbody>
</table>
}
else
{
<h5 class="text-secondary m-1">There are no comments for this ticket yet..</h5>
}
</div>
</div>
</div>
@*END TABLE*@
</div>
<div class="text-center p-3">
<a asp-controller="Ticket" asp-route-Id="@Model.Ticket.Ticket_Id" asp-action="Create" class="btn btn-success btn-lg text-white w-30">Edit</a>
<a asp-controller="Ticket" asp-route-Id="@Model.Ticket.Ticket_Id" asp-action="Delete" class="btn btn-danger btn-lg text-white w-30">Delete</a>
</div>
<!-- Bootstrap core JavaScript-->
<script src="/TemplateInfo/vendor/jquery/jquery.min.js"></script>
<script src="/TemplateInfo/vendor/bootstrap/js/bootstrap.bundle.min.js"></script>
<!-- Core plugin JavaScript-->
<script src="/TemplateInfo/vendor/jquery-easing/jquery.easing.min.js"></script>
<!-- Custom scripts for all pages-->
<script src="/TemplateInfo/js/sb-admin-2.min.js"></script>
</body>
</html>
【问题讨论】：
标签： c# asp.net-mvc asp.net-core entity-framework-core