Modify BuildApiResponse in ASP.Net Web Api - asp.net

Question

I am new in ASP.NET MVC Web API. I am trying to modified the return JSon to this format
{
"Error": false,
"Status": 200,
"Response": []
}
Now I able to do that by follow this post https://www.devtrends.co.uk/blog/wrapping-asp.net-web-api-responses-for-consistency-and-to-provide-additional-information . But the problem is I not able to show ModelState error like 'First name is required' because the code only show the first hit error.
if (error != null)
{
content = null;
//only show the first error
errorMessage = error.Message;
}
So I did some modification, now the code is written as below:
if (error != null)
{
content = null;
foreach(var e in error)
{
//if the error's type is ModelState
if (e.Key.Equals("ModelState"))
{
var allErrors = e.Value;
foreach (var modelError in (IEnumerable<KeyValuePair<string, object>>)allErrors)
{
var msg = modelError;
errorMessage = string.Concat(errorMessage, ", ", ((String[]) modelError.Value)[0]);
}
}
else
{
errorMessage = e.Value.ToString();
}
}
}
Now it's able to show all errors but the code is messy. I am writing this questions to find out what is the proper way to write this kind of code.

Answer 1

You can iterate over all the errors and concatenate them using StringBuilder. String.Join is much faster than Append for less than 1000 items (it is unlikely you will have so many errors in the modelstate object):
public static ValidationResult CheckValid(ModelStateDictionary modelState, string httpName = null)
{
if (!modelState.IsValid)
{
var sb = new StringBuilder();
sb.AppendLine(httpName + " failed: Invalid Json:");
foreach (var pair in modelState)
{
var error = String.Join(";", pair.Value.Errors.Select
(
i =>
{
if (!String.IsNullOrEmpty(i.ErrorMessage))
return i.ErrorMessage;
return i.Exception.Message;
}
));
sb.AppendLine($"Property: {pair.Key} Errors: ({error})");
}
return new ValidationResult(false, sb.ToString());
}
else
return new ValidationResult(true, "");
}