Posting ViewModel to MVC Controller - Still Cannot Get Working

Question

Sorry to bother everyone again with this repost, but I am still having problems getting my code to work. Essentially, what I am trying to understand is how to post a ViewModel back to a controller and ultimately, log it to a database. The receiving controller will need to accept

public List<tbl_Log_ReviewOfSystems>

The Controller:

        [HttpPost]
        public IActionResult InsertReviewOfSystems(ReviewOfSystemsVM model)
        {

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

        }

Posted data example:

EnteredBy: Someone

[0].ClientID: 1

[0].QuestionID: 8112

[0].CategoryCode: 1

[0].Category: General

[0].EnglishDescription: BMI

[0].QuestionResponse: None

[1].ClientID: 1

[1].QuestionID: 2092

[1].CategoryCode: 1

[1].Category: General

[1].EnglishDescription: BODYACHES

[1].QuestionResponse: None

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

Changing ViewModel to:

public List<tbl_Log_ReviewOfSystems>? ReviewOfSystems { get; set; } = new List<tbl_Log_ReviewOfSystems>() { };

returns 0. EnteredBy returns correct value in both scenarios. What am I doing wrong?

Answer 1

but I am still having problems getting my code to work. Essentially, what I am trying to understand is how to post a ViewModel back to a controller and ultimately, log it to a database. The receiving controller will need to accept

The problem is due to not following the model binding naming convention. The data model example (post parameter names) maps to List<tbl_Log_ReviewOfSystems> not ReviewOfSystemsVM. The input names are missing "tbl_Log_ReviewOfSystems" in the post parameter names. Therefore the model binder is unable to map the parameter name to the model property name.

The post parameters should have the naming convention below. As you can see, the parameter names are using the same "dot" syntax that C# uses.

EnteredBy: Hello World
tbl_Log_ReviewOfSystems[0].ClientID: 1
tbl_Log_ReviewOfSystems[0].VisitID: 9999999
tbl_Log_ReviewOfSystems[0].MRNumber: 5396
tbl_Log_ReviewOfSystems[0].QuestionID: 8112
tbl_Log_ReviewOfSystems[0].CategoryCode: 1
tbl_Log_ReviewOfSystems[0].Category: General
tbl_Log_ReviewOfSystems[0].EnglishDescription: BMI
tbl_Log_ReviewOfSystems[0].QuestionResponse: None
tbl_Log_ReviewOfSystems[1].ClientID: 1
tbl_Log_ReviewOfSystems[1].VisitID: 9999999
tbl_Log_ReviewOfSystems[1].MRNumber: 5396
tbl_Log_ReviewOfSystems[1].QuestionID: 2092
tbl_Log_ReviewOfSystems[1].CategoryCode: 1
tbl_Log_ReviewOfSystems[1].Category: General
tbl_Log_ReviewOfSystems[1].EnglishDescription: BODYACHES
tbl_Log_ReviewOfSystems[1].QuestionResponse: None

Unfortunately, you did not provide the code causing the problem. We have no idea how your code works and cannot provide an accurate solution.

Example View.

@model ReviewOfSystemsVM

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

<h1>Index</h1>

<form method="post" action="/SystemReview/InsertReviewOfSystems1">
    @Html.TextBoxFor(model => model.EnteredBy)
    <table class="table">
        <thead>
            <tr>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].ClientID)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].VisitID)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].MRNumber)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].QuestionID)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].CategoryCode)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].Category)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].EnglishDescription)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].QuestionResponse)
                </th>
                <th>
                    @Html.LabelFor(model => Model.tbl_Log_ReviewOfSystems[0].DateEntered)
                </th>
                <th></th>
            </tr>
        </thead>
        <tbody>
            @for (var i = 0; i < Model.tbl_Log_ReviewOfSystems.Count; i++)
            {
                <tr>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].ClientID)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].VisitID)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].MRNumber)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].QuestionID)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].CategoryCode)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].Category)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].EnglishDescription)
                    </td>
                    <td>
                        @Html.TextBoxFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].QuestionResponse)
                    </td>
                    <td>
                        @Html.DisplayFor(modelItem => Model.tbl_Log_ReviewOfSystems[i].DateEntered)
                    </td>
                </tr>
            }
        </tbody>
    </table>
    <div>
        <input type="submit" value="submit" />
    </div>
</form>

I want to point out that I provided an excellent blog that explains how the model binding naming convention works in your previous post. Please read the blog. There's is a lot of very good information that will help you move forward.

https://www.learnrazorpages.com/razor-pages/model-binding