asp.net mvc - Web API model binder doesn't work with HttpPostedFileBase?

Question

Testing out Web API for file uploading, have a simple view model like this:

public class TestModel {
    public string UserId {get;set;}
    public HttpPostedFileBase ImageFile {get;set;}
}

Used in the method:

[HttpPost]
public void Create(TestModel model)

When I attempt to post a multipart/form-data encoded form to the action, I receive this exception:

System.InvalidOperationException: No MediaTypeFormatter is available to read an object of type 'TestModel' from content with media type 'multipart/form-data'.
   at System.Net.Http.HttpContentExtensions.ReadAsAsync[T](HttpContent content, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger)
   at System.Net.Http.HttpContentExtensions.ReadAsAsync(HttpContent content, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger)
   at System.Web.Http.ModelBinding.FormatterParameterBinding.ReadContentAsync(HttpRequestMessage request, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger)
   at System.Web.Http.ModelBinding.FormatterParameterBinding.ExecuteBindingAsync(ModelMetadataProvider metadataProvider, HttpActionContext actionContext, CancellationToken cancellationToken)
   at System.Web.Http.Controllers.HttpActionBinding.<>c__DisplayClass1.<ExecuteBindingAsync>b__0(HttpParameterBinding parameterBinder)
   at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
   at System.Threading.Tasks.TaskHelpers.IterateImpl(IEnumerator`1 enumerator, CancellationToken cancellationToken) 

This works with the default MVC model binder, but apparently not with Web API's. Found some mentions that you can't use a view model when uploading a file, and to just separate the data into two calls. That doesn't work for me, since I need the other fields being posted in order to actually do something with the uploaded file. Is there a way to accomplish this?

Answer 1

You can either write a custom MediaTypeFormatter to facilitate your scenario or you can pull the data out of the request by hand using MultipartFormDataStreamProvider.FormData.AllKeys collection. This way you can post both the file(s) and additional fields in one request.

A good tutorial by Mike Wasson is available here: http://www.asp.net/web-api/overview/working-with-http/sending-html-form-data,-part-2