ASP.NET MVC posting current model to another index

Question

I have a form where a user can put in a date and view a table of data depending on the date. If the user wants to, he can download the data as a CSV file. This is my controller:

public class SomeController : Controller
{
    [HttpGet]
    public ActionResult Index()
    {            
        ModelClass model = new ModelClass();
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(ModelClass data)
    {
        if (data != null)
        {
            data.ReadData();

            return View(data);
        }
        else
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
    }

    [HttpPost]
    public FileContentResult DownloadCSV(ModelClass data)
    {
        if (data != null)
        {
            // generate CSV     
        }
        else
        {
           // ...
        }
    }
}

Basicly my GET-Index generates an empty model with default values (default date and data = null). Then via a form the user changes the date and submits the model to the POST-Index. There the function ReadData is executed, which generates the data within the model from a database-request and displays it in the View. If data is not null in the model the View displays a table with another form, which links to DownloadCSV. I would expect that the same model with my data would be posted to the DownloadCSV-site. But instead i get an empty model, which is not null, but without data. How can i accomplish my desired behavior and why is the described behavior to be expected?

Here is the View:

@using System.Data

@model Project.Models.ModelClass

@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Title</h2>


@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>SubTitle</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })

            <div class="form-group">
                @Html.LabelFor(model => model.Date, htmlAttributes: new { @class = "control-label col-md-4" })
                <div class="col-md-8">
                    <div class="input-group date">
                        @Html.EditorFor(model => model.Date, new { htmlAttributes = new { @class = "form-control form-date datecontrol", id = "datecontrol1" } })
                        <label class="input-group-addon btn" for="datecontrol1">
                            <i class="glyphicon glyphicon-calendar"></i>
                        </label>
                    </div>
                    @Html.ValidationMessageFor(model => model.Date, "", new { @class = "text-danger" })
                </div>
            </div>
        </div>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Submit" class="btn btn-default" />
            </div>
        </div>

    </div>
}

@if (Model.Data != null)
{
    <hr />

    <div class="pre-scrollable">
        <table class="table table-bordered table-responsive table-hover">
            <tr>
                <th style="white-space: nowrap; width: 1%;">Zeit</th>
                @foreach (DataColumn col in Model.Data.Columns)
                {
                    <th>@col.ColumnName</th>
                }
            </tr>

            @foreach (DataRow row in Model.Data.Rows)
            {
                <tr>
                    @foreach (DataColumn field in Model.Data.Columns)
                    {
                        if (field.ColumnName != "Zeit")
                        {
                            <td>@(row[field.ColumnName] != DBNull.Value ? Convert.ToDouble(row[field.ColumnName]).ToString("F1") : "0")</td>
                        }
                    }
                </tr>
            }
        </table>  
    </div>

    using (Html.BeginForm("DownloadCSV", "Some"))
    {
        @Html.AntiForgeryToken()

        <div class="form-group">
            <div class="col-md-offset-9 col-md-12">
                <input type="submit" value="Export CSV" class="btn btn-default" />
            </div>
        </div>
    }
}


@*<div>
    @Html.ActionLink("Back to List", "Index")
</div>*@

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

And the model:

public class ModelClass
{
    [Required]
    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:dd.MM.yyyy}", ApplyFormatInEditMode = true)]        
    public DateTime Date { get; set; }

    public DataTable Data { get; private set; }

    public ModelClass()
    {
        Date = DateTime.Now;
    }

    public void ReadData()
    {
        Data = new DataTable();

        // ... read data from database into datatable
    }
}

As you can see, Data should only be null if ReadData wasn't executed. So what i get in DownloadCSV is a just created instance of ModelClass.

Update:

I could solve the transfer of the Data field from the POST-Index to DownloadCSV without requesting the data again using TempData following this question: C# MVC pass data from one action method to another

Answer 1

Thanks to Stephen Mueckes comments and this SO question C# MVC pass data from one action method to another i could solve the problem the following way:

Updated Controller:

public class SomeController : Controller
{
    [HttpGet]
    public ActionResult Index()
    {            
        ModelClass model = new ModelClass();
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(ModelClass model)
    {
        model.ReadData();
        TempData['data'] = model.Data

        return View(data);
    }

    [HttpPost]
    public FileContentResult DownloadCSV(ModelClass model)
    {
        // model only has the date populated from the form, so take the data from TempData
        model.Data = TempData['data']

        // ... generate CSV     
    }
}

Updated View:

using (Html.BeginForm("DownloadCSV", "Some"))
{
    @Html.AntiForgeryToken()

    <div class="form-group">
        <div class="col-md-offset-9 col-md-12">
            @Html.HiddenFor(model => model.Date)
            <input type="submit" value="Export CSV" class="btn btn-default" />
        </div>
    </div>
}

This way, i store the results in TempData and don't have to request them again when i export a CSV. TempData will only be stored for the following request.