erlang mnesia 遍历

print_next(Current) ->
case mnesia:dirty_next(muppet, Current) of
'$end_of_table' ->
io:format("~n", []),
ok;
Next ->
[Muppet] = mnesia:dirty_read({muppet, Next}),
io:format("~p~n", [Muppet]),
print_next(Next),
ok
end.

print() ->
case mnesia:dirty_first(muppet) of
'$end_of_table' ->
ok;
First ->
[Muppet] = mnesia:dirty_read({muppet, First}),
io:format("~p~n", [Muppet]),
print_next(First),
ok
end.

dirty_all_keys

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edited Jan 11 at 11:31 Hamidreza Soleimani 1,286413

asked Oct 14 '11 at 6:14 Yola 4,65842848

traverse_table_and_show(Table_name)->
Iterator =  fun(Rec,_)->
io:format("~p~n",[Rec]),
[]
end,
case mnesia:is_transaction() of
true -> mnesia:foldl(Iterator,[],Table_name);
false ->
Exec = fun({Fun,Tab}) -> mnesia:foldl(Fun, [],Tab) end,
mnesia:activity(transaction,Exec,[{Iterator,Table_name}],mnesia_frag)
end.

muppet

traverse_table_and_show(muppet).

Iterator

http://www.erlang.org/doc/man/mnesia.html#foldl-3

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edited Aug 28 '15 at 23:44 Jesse Weigert 3,03521630

answered Oct 14 '11 at 8:53 Muzaaya Joshua 5,26532863

disc_only_copies

ets:tab2list(my_table).

io:format("~p~n", [ets:tab2list(my_table)]).

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answered Oct 14 '11 at 13:04 legoscia 22.5k84272

CatchAll = [{'_',[],['$_']}].
mnesia:dirty_select(TableName, CatchAll).

CatchAll = [{'_',[],['$_']}].
SelectFun = fun() -> mnesia:select(TableName, CatchAll) end.
mnesia:transaction(SelectFun).

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answered Oct 5 '14 at 15:05 Hamidreza Soleimani 1,286413

select_all() ->
mnesia:transaction(
fun() ->
P=qlc:e(qlc:q([E || E <- mnesia:table(tableName)])),      %query to select all data from table named 'tableName'
io:format(" ~p ~n ", [P]), % Prints table data on terminal
to_file("fileName.txt",P) % to_file method writes the data to file
end ).

to_file(File, L) ->
mnesia:transaction(
fun() ->
{ok, S} = file:open(File, write),
lists:foreach(fun(X) -> io:format(S, "~p.~n" ,[X]) end, L),
file:close(S)
end).