Posting Data to MVC Controller List Of

Question

Hello everyone and thanks for the help in advance. I'm trying to post data to a controller using a model that is a list. The controller:

        [HttpPost]
        public IActionResult InsertReviewOfSystems(List<tbl_Log_ReviewOfSystems> model)
        {

            return Content(model.Count.ToString());
        }

The model:

    public class tbl_Log_ReviewOfSystems
    {
        public int? ID { get; set; }
        public int? ClientID { get; set; }
        public int? VisitID { get; set; }
        public int? MRNumber { get; set; }
        public int? QuestionID { get; set; }
        public int? CategoryCode { get; set; }
        public string? Category { get; set; }
        public string? EnglishDescription { get; set; }
        public string? QuestionResponse { get; set; }
        public DateTime? DateEntered { get; set; } = DateTime.Now;
}

Sample data posted:

ClientID: 1

VisitID: 9999999

MRNumber: 5396

QuestionID: 8112

CategoryCode: 1

Category: General

EnglishDescription: BMI

QuestionResponse: None

EnteredBy: XXX

ClientID: 1

VisitID: 9999999

MRNumber: 5396

QuestionID: 2092

CategoryCode: 1

Category: General

EnglishDescription: BODYACHES

QuestionResponse: None

EnteredBy: XXX

The return from the controller is 500 error, NullReferenceException: Object reference not set to an instance of an object. Any help would be appreciated.

Answer 1

Your example data does not match the model or explain what is submitting the data. I'll assume a View posting an HTML form. The element names in the form must be indexed so the model binder can populate the list. https://www.learnrazorpages.com/razor-pages/model-binding

    public class SystemReviewController : Controller
    {
        public IActionResult Index()
        {
            List<tbl_Log_ReviewOfSystems> list = PopulateList();
            return View(list);
        }
        [HttpPost]
        public IActionResult InsertReviewOfSystems(List<tbl_Log_ReviewOfSystems> model)
        {

            return Ok(model);
        }

        private List<tbl_Log_ReviewOfSystems> PopulateList()
        {
            return new List<tbl_Log_ReviewOfSystems>() {
                new tbl_Log_ReviewOfSystems()
                {
                    ClientID = 1,
                    VisitID= 9999999,
                    MRNumber= 5396,
                    QuestionID= 8112,
                    CategoryCode= 1,
                    Category= "General",
                    EnglishDescription= "BMI",
                    QuestionResponse= "None",
                    DateEntered= DateTime.Now,
                },
                new tbl_Log_ReviewOfSystems()
                {
                    ClientID = 1,
                    VisitID= 9999999,
                    MRNumber= 5396,
                    QuestionID= 2092,
                    CategoryCode= 1,
                    Category= "General",
                    EnglishDescription= "BODYACHES",
                    QuestionResponse= "None",
                    DateEntered= DateTime.Now,
                }
            };
        }
    }

@model List<MvcDemo.Models.tbl_Log_ReviewOfSystems>

@{
    ViewData["Title"] = "Index";
}

<h1>Index</h1>

<form method="post" action="/SystemReview/InsertReviewOfSystems">
    <table class="table">
        <thead>
            <tr>
                <th>
                    @Html.LabelFor(model => Model[0].ClientID)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].VisitID)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].MRNumber)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].QuestionID)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].CategoryCode)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].Category)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].EnglishDescription)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].QuestionResponse)
                </th>
                <th>
                    @Html.LabelFor(model => Model[0].DateEntered)
                </th>
                <th></th>
            </tr>
        </thead>
        <tbody>
            @for (var i = 0; i < Model.Count; i++)
            {
                <tr>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].ClientID)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].VisitID)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].MRNumber)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].QuestionID)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].CategoryCode)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].Category)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].EnglishDescription)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model[i].QuestionResponse)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => Model[i].DateEntered)
                    </td>
                </tr>
            }
        </tbody>
    </table>
    <div>
        <input type="submit" value="submit" />
    </div>
</form>

Answer 2

Hi @Kmcnet,

NullReferenceException: Object reference not set to an instance of an object.

The error is because you haven't defined Model in your View.
You need to fill your model and send it to the View.

From the information you have provided so far, it is unclear how you implemented the post data. It would be best if you could provide more detailed information.

 [HttpGet]
        public IActionResult InsertReviewOfSystems()
        {
            
            return View(new List<tbl_Log_ReviewOfSystems>());
        }

Best regards,
Lan Huang

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