public string SaveCourseAssignManager(CourseAssignModel courseAssignModel)
 {
     if (courseAssignGateway.IsExistCourseGateway(courseAssignModel) == null)
     {
         if (courseAssignGateway.SaveCourseAssignGateway(courseAssignModel) > 0)
         {
             return("Save Successfull");
         }
         else
         {
             return("Save Fail");
         }
     }
     else
     {
         return(courseAssignGateway.IsExistCourseGateway(courseAssignModel));
     }
 }