How to return a error message in json result in C#?

Question

This is my code:

    [HttpPost]
    [Route("api/bulkUpload")]
    [IgnoreAntiforgeryToken]
    public JsonResult bulkUpload(IFormFile file)
    {
        List<Input> inputs = new List<Input>();
        try
        {
            var extension = Path.GetExtension(file.FileName);
            if (extension == ".csv")
            {
              .
              .
              .
            }
        }
        catch(exception ex)
        {
          return json(new { errormessage ="invalid file extension"});
        }
     return jsonresult(inputs)
    }

In swagger api if I give a different file(diff extensions) like .txt or .xls it is giving error code:500. But I want to return a error message as invalid file extension. PLease help on this code.

Answer 1

This may depend a bit on what version of ASP.NET you are using, but you should be able to do something like:

[Microsoft.AspNetCore.Mvc.Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{

    [Microsoft.AspNetCore.Mvc.HttpPost]
    [Microsoft.AspNetCore.Mvc.Route("api/bulkUpload")]
    [IgnoreAntiforgeryToken]
    public IActionResult bulkUpload(IFormFile file)
    {
        List<Input> inputs = new List<Input>();
        try
        {
            var extension = Path.GetExtension(file.FileName);
            if (extension == ".csv")
            {
                // do the thing!
            }
        }
        catch (Exception ex)
        {
            return BadRequest("invalid file extension");
            // or try this:
            // return BadRequest(new JsonResult("invalid file extension"));
        }

        return new JsonResult("ok");
    }

}

public class Input
{

}

Here is the docs on it and some examples.