POST actions in [ApiController] in ASP.NET Core 2.1

Question

I have the following ASP.NET Core 2.1 Api controller:

[Route("api/[controller]")]
[ApiController]
public class ImagesController : ControllerBase
{
    [HttpPost("[action]")]
    public async Task<IActionResult> Upload([FromForm]ICollection<IFormFile> files)
    { ... }

    [HttpGet("thumbnails")]
    public async Task<IActionResult> GetThumbNails()
    { ... }

Both the GET and POST actions worked with Postman.

However, the POST action would not work with the UI: the action would always receive a files parameter count of 0 (see here for full details of the fault).

I eventually fixed the fault by removing the [ApiController] attribute from the controller:

[Route("api/[controller]")]
//[ApiController]
public class ImagesController : ControllerBase
{ ... }

My question is why did the [ApiController] controller attribute prevent the POST method from receiving the files from the UI? What is happening here? Is it a routing problem?

Thieme · Accepted Answer · 2018-08-03 11:38:07Z

3

You need to set the compatibility version:

services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

According to https://learn.microsoft.com/en-us/aspnet/core/web-api/?view=aspnetcore-2.1

answered Aug 3, 2018 at 11:38

Thieme

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2 Comments

Thieme Over a year ago

Aha np :) I had almost the same issue today, so I found your question. Adding this fixed it for me. Maybe it will help other people.

MissRaphie Over a year ago

Fixed it for me, but I also add to add the following to the params for a single file upload public async Task<ActionResult> upload([FromForm(Name="uploadedFileName")]IFormFile uploadedFileName)

Mark G · Accepted Answer · 2018-06-19 02:26:55Z

3

The ApiController Attribute was added in ASP.NET Core 2.1 and includes binding source parameter inference. There is a recent commit to Infer BindingSource.FormFile for IEnumerable which may be related.

answered Jun 19, 2018 at 2:26

Mark G

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3 Comments

Winthorpe Over a year ago

I read that part of the guidance when I upgraded my project from Core 2.0 -> Core 2.1. So are you saying it is a fault?

Mark G Over a year ago

I can't say for sure, but you could try .NET Core 2.1.1 and see if it resolves your issue.

Eliseo Over a year ago

[ApiController] check if the ModelState is Valid (else give you a 400 response)

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