How to use currency format in ASP.NET MVC model in both display mode and when saving data

Question

In my ASP.NET MVC Core Code First project, I have a model with a property SaleAmount of type float that I'm successfully displaying in a currency format but when I save data using this property I get this field as null in SQL Server Database. In debug mode, when I place a breakpoint on this line oAnnualSales.SaleAmount = item.SaleAmount; in controller (shown below) I can see item.SaleAmount is null.

View:

public class AnnualSale
{    @model IList<MyProj.Models.SaleViewModel>
<div class="row">
    <div class="col-md-9">
        <form asp-controller="DbRelated" asp-action="UpdateSales" asp-route-returnurl="@ViewData[" ReturnUrl"]" method="post">
            <table class="table">
                <thead>
                    <tr>
                        <th></th>
                        <th>
                            State Name
                        </th>
                        <th>
                            Sale Amount
                        </th>
                    </tr>
                </thead>
                <tbody>
                    @for (int i = 0; i < Model.Count(); i++)
                    {
                    <tr>
                        <td>@Html.HiddenFor(r => r[i].StateId)</td>
                        <td>
                            @Html.EditorFor(r => r[i].StateName)
                        </td>
                        <td>
                            @Html.EditorFor(r => r[i].SaleAmount)
                        </td>
                    </tr>
                    }
                </tbody>
            </table>
            <button type="submit" class="btn btn-default">Save</button>
        </form>
    </div>
</div>
    [Key]
    public int Sale_Id { get; set; }
    public int? FiscalYear { get; set; }

    [DisplayFormat(DataFormatString = "{0:C0}", ApplyFormatInEditMode = true)]
    public float? SaleAmount { get; set; }

    public int StateId { get; set; }
    public StateName StateName { get; set; }
}

Model:

public class AnnualGrant
{
    [Key]
    public int Sale_Id { get; set; }

    public int? FiscalYear { get; set; }

    [DisplayFormat(DataFormatString = "{0:C0}", ApplyFormatInEditMode = true)]
    public float? SaleAmount { get; set; }

    public int StateId { get; set; }
    public StateName StateName { get; set; }
}

Controller:

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> UpdateSales(List<SaleViewModel> model, string returnUrl = null)
{
    if (ModelState.IsValid)
    {
        foreach (var item in model)
        {
            var oAnnualSales = _context.AnnualSales.Where(r => r.StateId.Equals(item.StateId)).FirstOrDefault();
            if (oAnnualSales != null)
            {
                oAnnualSales.FiscalYear = item.FY;
                oAnnualSales.SaleAmount = item.SaleAmount;
            }
            else
            {
                AnnualSale oAnnualSaleNew = new AnnualSale { StateId = item.StateId, FiscalYear = item.FY, SaleAmount = item.SaleAmount};
                _context.Add(oAnnualSaleNew);
            }
        }
        await _context.SaveChangesAsync();
        return View(model);
    }

    // If we got this far, something failed, redisplay form
    return View();
}

Answer 1

As mentioned in the comment to your question, posting characters such as currency symbols with the value will not parse to a float?, So will revert to null. You can test that by writing a quick unit test or console app which uses float.TryParse, which will return 0. You would need to either (not recommended) change the amount to a string, or (recommended) have the currency type and amount as different properties. Posting the currency symbol with the amount also relies on the user entering the currency symbol, which is unlikely to happen

Answer 2

This is not supported by default in ASP.NET MVC, but you can work around it with a custom model binder.

You first need to create a new class for the custom model binding:

public class FloatModelBinder : IModelBinder
{
  public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
  {
    ValueProviderResult valueResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
    ModelState modelState = new ModelState { Value = valueResult };
    object actualValue = null;
    try
    {
      if (bindingContext.ModelMetadata.EditFormatString.StartsWith("{0:c", StringComparison.InvariantCultureIgnoreCase))
      {
        actualValue = float.Parse(valueResult.AttemptedValue, NumberStyles.Currency);
      }
      else
      {
        actualValue = float.Parse(valueResult.AttemptedValue, CultureInfo.CurrentCulture);
      }
    }
    catch (FormatException e)
    {
      modelState.Errors.Add(e);
    }
    bindingContext.ModelState.Add(bindingContext.ModelName, modelState);
    return actualValue;
  }
}

Then you need to add this to the MVC binders by adding it to the Application_Start method:

protected void Application_Start()
{
  ModelBinders.Binders.Add(typeof(float?), new FloatModelBinder());    
}