public async Task <ActionResult> DeleteTrainer(int id)
{
try {
await _manager.DeleteTrainer(id);
return(RedirectToAction(nameof(ShowTrainers)));
}
catch (ArgumentNullException) {
return(RedirectToAction("ErrorPage", nameof(Main), new { message = "Error: can not delete trainer", call = nameof(Trainer) }));
}
catch (DbUpdateException) {
return(RedirectToAction("ErrorPage", nameof(Main), new { message = "Error: invalid input", call = nameof(Trainer) }));
}
}