how to handle a transaction with mnesia

mnesia:transaction.erl

{atomic, Result} = mnesia:transaction(Fun)
  case Result of [] -> undefined [Rec] -> Rec#rec.prop end.

%% http://www.erlang.org/doc/man/mnesia.html#transaction-2
add_family({family, F, M, Children}) ->
    ChildOids = lists:map(fun oid/1, Children),
    Trans = fun() ->      
        mnesia:write(F#person{children = ChildOids}, 
        mnesia:write(M#person{children = ChildOids},
        Write = fun(Child) -> mnesia:write(Child) end,
        lists:foreach(Write, Children)
    end,
    mnesia:transaction(Trans).
oid(Rec) -> {element(1, Rec), element(2, Rec)}.