public string Save(EnrollCourse aEnrollCourse)
 {
     if (aEnrollGateway.IsEnrollmentExists(aEnrollCourse))
     {
         return("One Student Enroll A Course Once only");
     }
     else
     {
         int rowAffected = aEnrollGateway.Save(aEnrollCourse);
         if (rowAffected > 0)
         {
             return("Enroll Successfull");
         }
         else
         {
             return("Failed");
         }
     }
 }