template <class TBL ,class ID, class NAME,int CLEARTIME>
struct ConvDict : Convert
{
	virtual Value Format(const Value& q) const {
		if(q.IsNull()) return Null;
		static VectorMap<int, String> dict;
		static Time lastcleartime;
		if(GetSysTime()-lastcleartime > CLEARTIME){
			dict.Clear();
			lastcleartime=GetSysTime();
		}
		int f = dict.Find(int(q));
		if(f >= 0){
			return dict[f];
		} else {
			Sql sql;
			sql * Select(NAME).From(TBL).Where(ID == q);
			String s;
			if(sql.Fetch()) {
				int sid = int(q);
				s = sql[NAME];
				dict.Add(sid, s);
			} else {
				s = "";
			}
			return s;
		}
	}
};