How to save Invoice Header and invoice rows on single page submit form with .net core razor pages? – Html

1.Explaination

I want to open the "Create" page, fill the invoice header data, fill the invoice dynamic rows data and save everything on one single submit.

(* Updated code)
I managed to solve the RowList error, which did not let me add multiple rows:

How to insert multiple rows with AddRange in ASP.NET Core Razor pages

Now i am getting an error

1.1 The error

ArgumentNullException: Value cannot be null. (Parameter ‘source’)

System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)

ArgumentNullException: Value cannot be null. (Parameter ‘source’)

System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
System.Linq.Enumerable.Count<TSource>(IEnumerable<TSource> source)
EPIDENT5.Pages.Magazina.Pages_Magazina_Create.<ExecuteAsync>b__28_0() in Create.cshtml

…

                @for (int i = 0; i < Model.RowList.Count(); i++)

Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext.GetChildContentAsync(bool useCachedResult, HtmlEncoder encoder)
Microsoft.AspNetCore.Mvc.TagHelpers.RenderAtEndOfFormTagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)
Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.g__Awaited|0_0(Task task, TagHelperExecutionContext executionContext, int i, int count)
EPIDENT5.Pages.Magazina.Pages_Magazina_Create.ExecuteAsync() in Create.cshtml

    ViewData["Title"] = "Create";

I know i am missing something but can not understand where the problem is.

2.Question

How can this be done?

3. The frontend code:

<form method="post">
                <div asp-validation-summary="ModelOnly" class="text-danger"></div>


// This is the header table 



                <table class="table table-striped border-0"
                       style="width: 100%; text-align: left;">
                    <thead class="border-0">

 <tr class="border-0">
                    <td class="border-0" style="min-width:100%;">
                        <div class="border border-secondary p-4">
                            <div class="row ">
                                <div style="float:left;width:50%;">
                                    <div class="form-group m-1">
                                        <label asp-for="InvHeader.Cli" class="control-label" style="font-size:80%;">Client</label>
                                        <input asp-for="InvHeader.Cli" class="form-control" value="clients name" />
                                    </div>
                                </div>
                                <div style="float:left;width:25%;">
                                    <div class="form-group m-1">
                                        <input asp-for="InvHeader.InvDate" class="form-control" type="date" value="@(DateTime.UtcNow.Date.ToString("yyyy-MM-dd"))" />
                                        <span asp-validation-for="InvHeader.InvDate" class="text-danger"></span>
                                    </div>
                                </div>
                                <div style="float:left;width:25%;">
                                    <div class="form-group m-1">
                                        <input asp-for="InvHeader.InvNr" class="form-control" value="33" />
                                        <span asp-validation-for="InvHeader.InvNr" class="text-danger"></span>
                                    </div>
                                </div>
                            </div>
                        </div>
                    </td>
                </tr>
                    </thead>
                </table>



//This is the dynamic rows table



 <table id="table1" border="0">
            <tr style="font-size:80%;">                  
                <th style="width:50%;">Product</th>
                <th style="width:5%;">qty</th>
                <th style="width:5%;">price</th>
            </tr>
                        foreach (var item in Model.PL)
                {
                    <tr class="border-bottom">                           
                        <td>
                            <select id="Products" asp-for="@Model.PL[@i].ProdId" class="form-control" type="text" name="data[@i][ProdId]" style="width:100%;"    >
                              
                                @foreach (var item in Model.PL)
                                {
                                    <option    value="@item.ProdId"    
                                            qty="@qty"
                                        price="@Convert.ToInt32(item.price)">@item.name,   @Convert.ToInt32(item.price)</option>
                                }
                            </select>
                        </td>
                        <td><input asp-for="@Model.MR[@i].qty" class="form-control" type="text" name="qty[@i]" style="width:100%;" /></td>
                                <td><input asp-for="@Model.MR[@i].price" class="form-control" type="text" name="price[@i]" style="width:100%;" /></td>
                     </tr>
                     </table>
                     
                     </form>

4.The backend code

//The data binding part

 [BindProperty]
    public InvHeader InvHeader { get; set; } = default!;
    public IList<InvRow> RowList { get; set; }

//The onget method, where row count id red

 public IActionResult OnGetAsync()
    {

        var rr = new List<InvRow>()
        {
            new InvRow() { Name = "Apple", Qty = 5, Price = 100 },
             new InvRow() { Name = "Peach", Qty = 3, Price = 500 },
              new InvRow() { Name = "Ananas", Qty = 1, Price = 1100 },
        };

        RowList = rr;

        return Page();
    }

//The Onpost method

public async Task<IActionResult> OnPostAsync(IList<InvRow> RowList)
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

         _context.InvHeaders.Add(InvHeader);

        await _context.InvRows.AddRangeAsync(RowList);

        await _context.SaveChangesAsync();

        return RedirectToPage("./Index");
    }