public string Invoke(string firstLater)
{
switch (firstLater)
{
case "m":
return(memberService.Count(null).ToString());
case "b":
return(bookService.Count(null).ToString());
case "r":
return(rentService.Count(a => a.isRentingCompleted == false).ToString());
case "u":
return(userService.Count(null).ToString());
default:
return("0");
}
}