Razor page add items to list and update partial views - not MVC

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C#

ASP.NET

Razor

I'm new to web app development, and I wonder if somebody could point me in the right direction with this? I think I know what the problem is, but I don't know how to fix it.

What I have is a complex model where a header can contain a child, and each child can itself have its own children (of different types).

My demo code shown here has a header, and two lists. If I click the button to add a child item to either the first list or a second list, the initial problem I have is that the items don't appear. The other problem is that I don't appear to be able to keep on adding items to either list.

To try to see what is going on, I added a section to show the innerHTML to see what the data is - and this illustrates that if I click to add to the first list, some data appears for the first list, but if I click to add to the second list, the new data disappears from the first list whilst the new item appears as expected in the second list.

I think the problem is that the Model isn't updated to reflect the new items - but I understand that we shouldn't be able to do that with Javascript anyway. So, I think I need to separate all my partial views, so I have a main partial view containing lots of partial views, and when my Ajax call is successful, refresh the MAIN partial view.

My PageModel

namespace ParentChildDemo.Pages
{
    public class IndexModel : PageModel
    {
        private readonly ILogger<IndexModel> _logger;

        [BindProperty]
        public Header MyHeader { get; set; } = new Header();

        public IndexModel(ILogger<IndexModel> logger)
        {
            _logger = logger;
        }

        public void OnGet()
        {
            MyHeader.Id = 1;
            MyHeader.MyHeaderProperty = "HeaderTest1";
            MyHeader.ChildOfHeader.Add(new ChildOfHeader());

            for (int i = 1; i <= 3; i++)
            {
                var childOfChild = new ChildOfChild()
                {
                    Id = i,
                    HeaderId = MyHeader.Id,
                    MyChildProperty = $"FirstChildTest{i}"
                };

                MyHeader.ChildOfHeader[0].MyFirstChildList.Add(childOfChild);
            }

            for (int i = 1; i <= 2; i++)
            {
                var childOfChild = new ChildOfChild()
                {
                    Id = i,
                    HeaderId = MyHeader.Id,
                    MyChildProperty = $"SecondChildTest{i}"
                };

                MyHeader.ChildOfHeader[0].MySecondChildList.Add(childOfChild);
            }
        }

        public PartialViewResult OnPostAddNewFirstListChildItem([FromBody] Header myHeader)
        {
            if (myHeader.ChildOfHeader[0].MyFirstChildList == null)
                myHeader.ChildOfHeader[0].MyFirstChildList = new List<ChildOfChild>();

            var childId = myHeader.ChildOfHeader[0].MyFirstChildList.Count + 1;

            myHeader.ChildOfHeader[0].MyFirstChildList.Add(new ChildOfChild
            {
                Id = childId,
                HeaderId = myHeader.Id,
                MyChildProperty = $"FirstChildTest{childId}"
            });

            var partialView = "_ListPartialView";
            //var partialView = "_FirstListItemPartial";

            var data = new IndexModel(_logger);
            data.MyHeader = myHeader;

            var myViewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()) { { partialView, myHeader } };
            //var myViewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()) { { partialView, myHeader.ChildOfHeader[0].MyFirstChildList } };
            myViewData.Model = data;

            var partialViewResult = new PartialViewResult()
            {
                ViewName = partialView,
                ViewData = myViewData,
            };

            return partialViewResult;
        }

        public PartialViewResult OnPostAddNewSecondListChildItem([FromBody] Header myHeader)
        {
            if (myHeader.ChildOfHeader[0].MySecondChildList == null)
                myHeader.ChildOfHeader[0].MySecondChildList = new List<ChildOfChild>();

            var childId = myHeader.ChildOfHeader[0].MySecondChildList.Count + 1;

            myHeader.ChildOfHeader[0].MySecondChildList.Add(new ChildOfChild
            {
                Id = childId,
                HeaderId = myHeader.Id,
                MyChildProperty = $"SecondChildTest{childId}"
            });

            var partialView = "_ListPartialView";
            //var partialView = "_SecondListItemPartial";

            var data = new IndexModel(_logger);
            data.MyHeader = myHeader;

            var myViewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()) { { partialView, myHeader } };
            //var myViewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()) { { partialView, myHeader.ChildOfHeader[0].MySecondChildList } };
            myViewData.Model = data;

            var partialViewResult = new PartialViewResult()
            {
                ViewName = partialView,
                ViewData = myViewData,
            };

            return partialViewResult;
        }
    }

    public class Header
    {
        public int Id { get; set; }
        public string MyHeaderProperty { get; set; }
        public List<ChildOfHeader> ChildOfHeader { get; set; } = new List<ChildOfHeader>();
    }

    public class ChildOfHeader
    {
        public List<ChildOfChild> MyFirstChildList { get; set; } = new List<ChildOfChild>();
        public List<ChildOfChild> MySecondChildList { get; set; } = new List<ChildOfChild>();
    }

    public class ChildOfChild
    {
        public int Id { get; set; }
        public int HeaderId { get; set; }
        public string MyChildProperty { get; set; }
    }
}

My Index page

@page
@model IndexModel
@{
    ViewData["Title"] = "Home page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>Learn about <a href="https://docs.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>
</div>

<div>
    <a class="btn btn-sm btn-info text-white" onclick="AddListItem(1)">Add Child to First list</a>
    <a class="btn btn-sm btn-info text-white" onclick="AddListItem(2)">Add Child to Second list</a>
</div>

<br />

<div>
    <div>MyHeaderProperty value: @Model.MyHeader.MyHeaderProperty</div>
    <br />
    <div class="container">
        <div class="row">
            <div class="col-6 font-weight-bold">First List</div>
            <div class="col-6 font-weight-bold">Second List</div>
        </div>
        <div class="ListPartialView">
            <partial name="_ListPartialView" model="@Model" />
        </div>
    </div>
    <br />
    <div class="bg-warning" id="HtmlContent"></div>
    
    @Html.AntiForgeryToken()
</div>

<script type="text/javascript">
    function AddListItem(listNumber) {
        var model = @Json.Serialize(Model.MyHeader);

        var handler;
        var partialView;

        if (listNumber == 1) {
            handler = "?handler=AddNewFirstListChildItem";
            partialView = "#ListPartialView";//"#FirstListPartial";
        }
        else {
            handler = "?handler=AddNewSecondListChildItem";
            partialView = "#ListPartialView";//"#SecondListPartial";
        }

        $.ajax({
            type: "POST",
            url: handler,
            data: JSON.stringify(model),
            dataType: "html",
            contentType: "application/json",
            headers: {
                RequestVerificationToken: $('input:hidden[name="__RequestVerificationToken"]').val()
            },
            success: function (result) {
                document.getElementById("HtmlContent").innerHTML = result.toString();
                $(partialView).html(result);
            },
            failure: function (result) {
                alert("Failed");
            }
        });
    }
</script>

My Main partial view (_ListPartialView)

@model IndexModel

@for (int i = 0; i < Model.MyHeader.ChildOfHeader.Count; i++)
{
    ViewData["ChildIndex"] = i;

    <div class="row">
        <div id="FirstListPartial" class="col-6">
            <partial name="_FirstListItemPartial" model="@Model" view-data="ViewData" />
        </div>
        <div id="SecondListPartial" class="col-6">
            <partial name="_SecondListItemPartial" model="@Model" view-data="ViewData" />
        </div>
    </div>
}

My My first list partial view (_FirstListItemPartial)

@model IndexModel

@{ 
    var indexId = (int)ViewData["ChildIndex"];
}


<table>
    @foreach (var myChildItem in Model.MyHeader.ChildOfHeader[indexId].MyFirstChildList)
    {
        <tr>
            <td>@myChildItem.Id</td>
            <td>@myChildItem.MyChildProperty</td>
        </tr>
    }
</table>

My second list partial view (_SecondListItemPartial)

@model IndexModel

@{
    var indexId = (int)ViewData["ChildIndex"];
}

<table>
    @foreach (var myChildItem in Model.MyHeader.ChildOfHeader[indexId].MySecondChildList)
    {
        <tr>
            <td>@myChildItem.Id</td>
            <td>@myChildItem.MyChildProperty</td>
        </tr>
    }
</table>

What I have tried:

In my < script > I think I need to refer to my page, and not my Model every time one of the buttons is pressed. I have tried to serialize my partial view (ListPartialView), and I have changed my parameter type to 'dynamic' and removed the [FromBody], but my object content is is always {object} - not the page data (from what I can make out).