How can I customize the error response in Web API with .NET Core?

Question

I am using .NET Core 2.2 with Web API. I have created one class, i.e., as below:

public class NotificationRequestModel
{
    [Required]
    public string DeviceId { get; set; }
    [Required]
    public string FirebaseToken { get; set; }
    [Required]
    public string OS { get; set; }

    public int StoreId { get; set; }
}

Using the above class I have created one method. Now I want to return a custom object, but it's returning its own object. API method is:

public ActionResult<bool> UpdateFirebaseToken(NotificationRequestModel model)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(FormatOutput(ModelState.Values));
    }
    var result = _notificationService.InsertOrUpdateFirebaseToken(model);
    return Ok(result);
}

Here FormatOutput method is format the output.

protected Base FormatOutput(object input, int code = 0, string message = "", string[] details = null)
{
    Base baseResult = new Base();
    baseResult.Status = code;
    baseResult.Error = message;
    baseResult.TimeStamp = CommonHelper.CurrentTimeStamp;
    baseResult.Code = code;
    baseResult.Details = details;
    baseResult.Message = message; //Enum.Parse<APIResponseMessageEnum>(code.ToString(), true); // (enum of code get value from language)
    return baseResult;
}

But the issue is it returns:

{
  "errors": {
    "DeviceId": [
      "The DeviceId field is required."
    ]
  },
  "title": "One or more validation errors occurred.",
  "status": 400,
  "traceId": "80000049-0001-fc00-b63f-84710c7967bb"
}

I want to customize this error with my model. I need error message and details from return output and passed it to my model. How can I do that? I had try to debug my code and found that breakpoint on API method is not calling. So I can't handle my custom method. Is there any solution? What am I doing wrong?

Answer 1

As Chris analyzed, your issue is caused by Automatic HTTP 400 responses.

For the quick solution, you could suppress this feature by

services.AddMvc()
        .ConfigureApiBehaviorOptions(options => {
            options.SuppressModelStateInvalidFilter = true;
        }).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

For an efficient way, you could follow the suggestion from Chris, like below:

services.AddMvc()
        .ConfigureApiBehaviorOptions(options => {
            //options.SuppressModelStateInvalidFilter = true;
            options.InvalidModelStateResponseFactory = actionContext =>
            {
                var modelState = actionContext.ModelState.Values;
                return new BadRequestObjectResult(FormatOutput(modelState));
            };
        }).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

And, there isn't any need to define the code below any more in your action.

if (!ModelState.IsValid)
{
    return BadRequest(FormatOutput(ModelState.Values));
}