How to put a file upload button optional in asp.net c# applications?

Question

I have a basic asp.net c# application which has a form to submit some data to database, This form has an upload button to upload a file.

Initially, there was a problem that: i was not able to submit a form without uploading a file, it was giving an error as [object reference not set to an instance of an object], which means uploading a file was a must before submitting the form, So to resolve that issue i made some changes in my controller.

Now it submits the form even if i don't upload anything, but the new problem is that when i upload a file and submit then it still submits the form successfully but it does not upload the actual file.

This is the model:

  public class Events
{
    public int Id { get; set; }
    public string title { get; set; }
    public string amount { get; set; }
    public string Finance_Approval { get; set; }
    public DateTime date_time { get; set; }

    public string file_one { get; set; }
    [NotMapped]
    public HttpPostedFileBase file1 { get; set; }
}

This is the controller:

    public ActionResult Index()
    {  
        return View();
    }


   public ActionResult Request(Events e)
    {
        if (e.file_one==null)
        {
            _context.evt.Add(e);
            _context.SaveChanges();

            return Content("Added");
        }

        else
        {
            string filename = Path.GetFileNameWithoutExtension(e.file1.FileName);
            string extension = Path.GetExtension(e.file1.FileName);
            filename = filename + DateTime.Now.ToString("yymmssfff") + extension;
            e.file_one = "PM_Files/" + filename;
            filename = Path.Combine(Server.MapPath("~/PM_Files/"), filename);
            e.file1.SaveAs(filename);

            _context.evt.Add(e);
            _context.SaveChanges();

            return Content("Added");
        }

    }

And this is the razor view:

@using (Html.BeginForm("Request", "Requester", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
    <div class="form-group">
        @Html.LabelFor(a => a.title)
        @Html.TextBoxFor(a => a.title, new { @class = "form-control" })
    </div>
    <div class="form-group">
        @Html.LabelFor(a => a.amount)
        @Html.TextBoxFor(a => a.amount, new { @class = "form-control" })
    </div>
    <div class="form-group">
        <label>Select the file word or pdf etc</label>
        <input type="file" name="file1" />
    </div>    
    <button class="btn btn-primary">Request</button>
}

Your file is being uploaded, but you do not have a form control for file_one so its always null - you else block will never be executed — user3559349
– user3559349, Commented Nov 14, 2018 at 4:52
You need this one: @Html.TextBoxFor(a => a.file_one, new { @class = "form-control", @readonly = "readonly" }) to store the file name. In your current code this textbox doesn't exist, hence the filename is never captured. — Tetsuya Yamamoto
– Tetsuya Yamamoto, Commented Nov 14, 2018 at 4:55
@StephenMuecke you mean to say that i have to add the form-control class in upload button and it will resolve the issue — John Kamaal
– John Kamaal, Commented Nov 14, 2018 at 4:56
No. You do not have a <input> element for file_one (nor should you). What you need to check is if e.file1 is null, not e.file_one` (and you also check the ContentLength) — user3559349
– user3559349, Commented Nov 14, 2018 at 4:59
if (e.file_one==null) => this is your problem, because you're checking against file_one string. You should check against file existence, i.e. HttpPostedFileBase. — Tetsuya Yamamoto
– Tetsuya Yamamoto, Commented Nov 14, 2018 at 4:59

Tetsuya Yamamoto · Accepted Answer · 2018-11-14 05:10:32Z

The exact problem is you're checking null against file_one string property, which always has null value because no form control associated with it inside view page. You should check against HttpPostedFileBase instead:

[HttpPost]
public ActionResult Request(Events e)
{
    if (e.file1 != null && e.file1.ContentLength > 0)
    {
        // save the file

        return Content("Added");
    }

    else
    {
        // do something else

        return Content("Added");
    }
}

If standard HttpPostedFileBase check above does not work, you should try Request.Files to get the file info:

[HttpPost]
public ActionResult Request(Events e)
{
    if (Request.Files.Count > 0)
    {
        foreach (string files in Request.Files)
        {
             if (!string.IsNullOrEmpty(files))
             {
                 // save the file
             }
        }

        return Content("Added");
    }

    else
    {
        // do something else

        return Content("Added");
    }
}

Notes:

1) The form uses FormMethod.Post, therefore the controller action should use [HttpPost] attribute.

2) [NotMapped] attribute is only used for data models to exclude entity mapping to column in database - it is not used in viewmodels, just remove it.

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