public async Task<HttpResponseMessage> InsertAsync(Exam exam)
 {
     if (exam != null)
     {
         return Request.CreateResponse(await examService.InsertAsync(exam) > 0 ? HttpStatusCode.OK : HttpStatusCode.BadRequest);
     }
     return Request.CreateResponse(HttpStatusCode.BadRequest);
 }
 public async Task<HttpResponseMessage> UpdateAsync(Exam exam)
 {
     var result = await examService.UpdateAsync(exam);
     if (result > 0)
     {
         return Request.CreateResponse(HttpStatusCode.OK);
     }
     return Request.CreateResponse(HttpStatusCode.BadRequest);
 }