Rest – How to upload file AND model using Web API

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Basically I'm trying to upload an image along with an enum using Web API 2.

Here's the controller signature:

[HttpPost]
public UploadResponseVm Upload([FromBody]ResImageType type)
{

The thing is, whenever I try to post a multipart form (with a file and a type) I get a 415 error:

{"Message":"The request entity's media type 'multipart/form-data' is
not supported for this resource.","ExceptionMessage":"No
MediaTypeFormatter is available to read an object of type
'ResImageType' from content with media type
'multipart/form-data'.","ExceptionType":"System.Net.Http.UnsupportedMediaTypeException","StackTrace":"
at System.Net.Http.HttpContentExtensions.ReadAsAsync[T](HttpContent
content, Type type, IEnumerable1 formatters, IFormatterLogger
formatterLogger, CancellationToken cancellationToken)\r\n at
System.Web.Http.ModelBinding.FormatterParameterBinding.ReadContentAsync(HttpRequestMessage
request, Type type, IEnumerable1 formatters, IFormatterLogger
formatterLogger, CancellationToken cancellationToken)"}

I have even added the following to my startup.cs class:

    config.Formatters.Insert(0, new System.Net.Http.Formatting.JsonMediaTypeFormatter());

How can I upload a model along with a file using a web api controller?

Best Answer

There is no formatter that could handle/relate to your ResImageType object. I have once solved a similar problem without a formatter by using a parameter-less method and have processed the data inside the method. For example:

public async Task<HttpResponseMessage> PostFormData()
    {
        if (!Request.Content.IsMimeMultipartContent("form-data"))
        {
            return Request.CreateResponse(HttpStatusCode.BadRequest);
        }

            string upDir= "PathOfDirectory";

            MultipartFormDataStreamProvider streamProvider = new MultipartFormDataStreamProvider(upDir);                
            MultipartFileStreamProvider multipartFileStreamProvider = await Request.Content.ReadAsMultipartAsync(streamProvider);

            // Loop through files.
            foreach (MultipartFileData file in streamProvider.FileData)
            {
                // Save filepaths to DB or do something else
            }
            return Request.CreateResponse(HttpStatusCode.OK);
    }

Similar solution from MS Docs

Another possibility is to create a DTO-like class that is used to transfer the object and use a formatter, for example MultipartDataMediaFormatter seems legit (haven't tried).

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