How to get all Errors from modelState in ASP.Net MVC?

[HttpPost]

public HttpResponseMessage Registration(RegistrationRequest reg)

{

    if (ModelState.IsValid)

    {

        return Request.CreateResponse(HttpStatusCode.OK);

    }

    IEnumerable<string> errors = ModelState.Values.SelectMany(v => v.Errors.Select(b => b.ErrorMessage));

    string strErrors = string.Join("; ", errors);

    return Request.CreateErrorResponse(HttpStatusCode.BadRequest, strErrors);

}

OR

[HttpPost]

public HttpResponseMessage Registration(RegistrationRequest reg)

{

    if (ModelState.IsValid)

    {

        return Request.CreateResponse(HttpStatusCode.OK);

    }

    return Request.CreateErrorResponse(HttpStatusCode.BadRequest, ModelState);

}