public static List <T> FetchManyToOne <T, T1, T2, T3>(this Database db, Func <T, object> key, Sql Sql)
        {
            var relator = new Relator();

            return(db.Fetch <T, T1, T2, T3, T>((a, b, c, d) => relator.ManyToOne(a, b, c, d, key), Sql));
        }
        public static List <T> FetchOneToMany <T, T1>(this Database db, Func <T, object> key, Sql Sql)
        {
            var relator = new Relator();

            return(db.Fetch <T, T1, T>((a, b) => relator.OneToMany(a, b, key), Sql));
        }