Question

This should be straight-forward, but here goes – we’re using MVC4 to handle a multi-part Form request to upload a binary along with some meta-data via a strongly-typed view in MVC4.

One of the fields is a version number for the file (i.e. something like 0.0.6, 0.4.5-pre, etc…)

I’m getting the following error from the model binder when it tries to bind this version number field to the model field (string type):

{“The parameter conversion from type ‘System.String’ to type
‘Models.NewFileVersion’ failed because no type converter can convert
between these types.”}

Specifically the error can be traced to our “VersionNumber” field – any ideas as to why this might be happening?

Edit: Source code below

NewFileVersion.cs

public class NewFileVersion
{
    [Display(Name = "Version # (0.67, 0.66-pre, etc...)")]
    [Required]
    public string Version { get; set; }

    [Required]
    [StringLength(2000, ErrorMessage = "ChangeLog must be between 30 an 2000 characters", MinimumLength = 30)]
    [Display(Name = "Version Notes (will be visible to end-users)")]
    [DataType(DataType.MultilineText)]
    public string ChangeLog { get; set; }

    [Display(Name = "Target Platform")]
    [UIHint("Enum")]
    public FileType PlatformTarget { get; set; }
}

New.cshtml

    @model ViewModels.NewFileVersion
@{
    ViewBag.Title = "New";
}
<div class="container" id="main-content">
    <div class="row">
        <h2>
            New</h2>
        @using (Html.BeginForm("Create", "Files", FormMethod.Post, new { enctype = "multipart/form-data" }))
        {
            @Html.ValidationSummary(true)

            <fieldset>
                <legend>NewFileVersion</legend>
                <div class="editor-label">
                    @Html.LabelFor(model => model.Version)
                </div>
                <div class="editor-field">
                    @Html.EditorFor(model => model.Version)
                    @Html.ValidationMessageFor(model => model.Version)
                </div>
                <div class="editor-label">
                    @Html.LabelFor(model => model.ChangeLog)
                </div>
                <div class="editor-field">
                    @Html.EditorFor(model => model.ChangeLog)
                    @Html.ValidationMessageFor(model => model.ChangeLog)
                </div>
                <div class="editor-label">
                    @Html.LabelFor(model => model.PlatformTarget)
                </div>
                <div class="editor-field">
                    @Html.EditorFor(model => model.PlatformTarget)
                </div>
                <div class="editor-label">
                    <label for="">
                        File:</label></div>
                <div class="editor-field">
                    <input type="file" name="fileData" required="required" /></div>
                <p>
                    <input type="submit" value="Upload File" />
                </p>
            </fieldset>
        }
        <div>
            @Html.ActionLink("Back to List", "Index")
        </div>
    </div>
</div>

FilesController.cs

 [HttpPost]
    public ActionResult Create(NewFileVersion version, HttpPostedFileBase fileData)
    {
        //if our model is valid
        if(ModelState.IsValid)
        {
            //etc....             
        }

        ModelState.AddModelError("", "Invalid file submission");

        return View("New", version);
    }

Answer 1

Try renaming the version parameter for your Create action, e.g:

public ActionResult Create(NewFileVersion fileVersion, HttpPostedFileBase fileData) { ... }

The model binder may be getting confused between the string version model property and the NewFileVersion version action parameter.

---

You can see why this happens in the BindModel method, because the model has a property exactly matching the name of the action parameter it tries to bind as a simple type/model rather than a complex one.