Question

Here is the POST action in my ApiController.

public HttpResponseMessage Post(ViewModel model)
    {
        if (!ModelState.IsValid)
        {
            var ResponseMessage = new HttpResponseMessage(HttpStatusCode.XXXXXX
            return ResponseMessage; 
        }

        if (!_service.Create(model))
        {
            var ResponseMessage=new HttpResponseMessage(HttpStatusCode.NotAcceptable);
            return ResponseMessage;
        }
        else
        {
            return new HttpResponseMessage(HttpStatusCode.Created);
        }
    }

Is it okay to enable server-side model validation in this way? And, I am pretty sure a Created should be returned if everything is fine. But what kind of HttpStatusCode should I return if the ModelState is invalid, or if some error occurs?

Answer 1

Normally it should be 400 – BadRequest.

NotAcceptable is when Accept headers cannot be satisfied by the server.

PreConditionFailed is when caching validation conditions fails. For example, if a PUT request requires update if and only if ETag match value in the request.

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Alternatively you may send custom error. Since it is to do with Request, you need to use 4xx numbers:

return new HttpResponseMessage((HttpStatusCode) 499) 
     {
          ReasonPhrase = "Validation failed"
     };