C# patterns subclasses -

i have class person, 2 child classes staff , student, interface iperson. have class database , class gateway. class database has

private string id = "username"; 

and method

public void getid() {return id;} 

both staff , student have getid() methods. gateway has check if method getid() requested staff (return id) or student (return "go away!"). can please me that. thinking using gateway interface of database class, because trying learn c#, don't know how that. or maybe there's better way of doing this... please thanks

here's code:

public class staff : person   {       public staff() {}     public staff(string id): base(id) {}     public override string getname()     {         throw new notimplementedexception();     }     public override void update(object o)     {       console.writeline(id + " notified {1}", id, o.tostring());      }     public override void updatemessage(object p)     {       console.writeline(id + " notified new message in chat: {1}", id, p.tostring());      }   } 

---

public class student : person {     public student() {}     public student(string id): base(id) {}     public override string getname()     {         throw new notimplementedexception();     }     public override void update(object o)      {      console.writeline(id +"  notified {1}", id, o.tostring());     }     public override void updatemessage(object p)      {      console.writeline("message " + id + "  {1}", id, p.tostring());     } } 

---

 public abstract class person : iperson {     string id;     public person() { }     public abstract string getname();     public person(string i) { this.id = i; }     public abstract void update(object o);     public abstract void updatemessage(object p); }  public interface iperson       {    void update(object o);    void updatemessage(object p);    string getname();  } 

---

 class database  {      public string username = "username";      private string name =  "user details";      private string grade = "user grade";       public string getname(object o)      {          if (o staff) { return name; }          else { return "go away!"; }      }      public string getgrade() { return grade; }  }    public class gateway    {     public void dosomethingwithperson(iperson person)     {         string id = person.getname();         if (person student)         {             return "go away!";         }         else if (person staff)         {             return name;         }     } } 

i discourage is chains altogether. violates liskov. in short, means hard add new iperson implementation without modifying gateway cope new type. or forces developers descend 1 of existing types implement new iperson, in case, point of interface on abstract person type?

public class gateway {  public string dosomethingwithperson(iperson person)  {     return person.dosomething();  } }  //then iperson implementors student can provide custom behaviour. public class student : person {   public string dosomething()   {        return "go away!";   }   ... }