Erlang：将 mnesia 表写入 .csv 每行一条记录

Question

我有一个 Mnesia 表，其格式如下：

-record(state, {key, tuple, state, timestamp, fin_from}).

条目如下所示（使用ets:tab2list(Tab) 阅读）：

[{state,{80,43252,tcp,tcp_syn_received,{192,168,101,5},{192,168,101,89}},
        {80,43252,tcp,{192,168,101,5},{192,168,101,89}},
        tcp_syn_received,1463850419221,undefined},
 {state,{80,41570,tcp,tcp_syn_received,{192,168,101,5},{192,168,101,89}},
        {80,41570,tcp,{192,168,101,5},{192,168,101,89}},
        tcp_syn_received,1463850403214,undefined},
...]

我想将这些数据写入 .csv 文件，每行一个条目 - 首选以下格式：

state,80,43252,tcp,tcp_syn_received,192.168.101.5,192.168.101.89,80,43252,tcp,192.168.101.5,192.168.101.89,tcp_syn_received,1463850419221,undefined
state,80,41570,tcp,tcp_syn_received,192.168.101.5,192.168.101.89,80,41570,tcp,192.168.101.5,192.168.101.89,tcp_syn_received,1463850419221,undefined

undefined 之后应该有一个换行符。 我尝试使用以下代码（Content = ets:tab2list(states)）：

do_logging_async(File, Format, Content, Append)->
F = fun() ->
    file:write_file(File, io_lib:fwrite(Format, [Content]), [Append])
end,
spawn(F).

但是，我无法获得与我的输出类似的任何内容。 之后应使用 R 评估数据。

更新：关键是逐行读取表格并用~w而不是~p解析它。我最终得到了以下解决方案（它产生的输出略有不同，但是冗余数据较少）：

do_state_logging(File, EtsAsList) ->
% write header (columnnames)
file:write_file(File, io_lib:fwrite("~w,~w,~w,~w,~w,~w,~w,~w~n", [record,dstPort,srcPort,proto,dstIP,srcIP,state,timestamp]),[append]),
case EtsAsList of
    [] ->
        ok;
    _ ->
        F = fun({Record,_Key, 
            [P1, P2, Proto, {D_Ip_1,D_Ip_2,D_Ip_3,D_Ip_4}, {S_Ip_1,S_Ip_2,S_Ip_3,S_Ip_4}],
            State, Timestamp, _}) -> 
            file:write_file(File, io_lib:fwrite("~w,", [Record]),[append]),
            file:write_file(File, io_lib:fwrite("~w,~w,~w,", [P1,P2,Proto]),[append]),
            file:write_file(File, io_lib:fwrite("~w.~w.~w.~w,", [D_Ip_1,D_Ip_2,D_Ip_3,D_Ip_4]), [append]),
            file:write_file(File, io_lib:fwrite("~w.~w.~w.~w,", [S_Ip_1,S_Ip_2,S_Ip_3,S_Ip_4]), [append]),
            file:write_file(File, io_lib:fwrite("~w,", [State]),[append]),
            file:write_file(File, io_lib:fwrite("~w", [Timestamp]),[append]),
            file:write_file(File, ["\n"],[append]) 
        end,
        lists:foreach(F, EtsAsList)
    end,
    io:format("Finished logging of statetable to file: ~p~n" , [File]).

感谢促使我提出这个想法的答案。

Answer 1

假设您将 ets 记录值更改为列表而不是元组，您可以使用此代码将 ETS 表写入文件。

do_logging_async(File, EtsAsList) ->
    F = fun({Key, Value}) -> 
        file:write_file(File, [atom_to_list(Key) ++ ","],[append]),
        write_value(File,lists:flatten(Value)),
        file:write_file(File, ["\n"],[append]) 
    end,
    lists:foreach(F,EtsAsList).


write_value(_File, []) -> ok;
write_value(File, [H|T]) ->
    case is_integer(H) of
        true -> file:write_file(File, [integer_to_list(H)],[append]);
        false -> file:write_file(File, [atom_to_list(H)],[append])
    end,
    case T=:=[] of
        true -> ok;
        false -> file:write_file(File, [","],[append])
    end,
    write_value(File,T).

do_logging_async/2 获取每个 {Key, Value} 对。首先，它将Key 写入文件，然后在Value 上运行write_value/2，在每对的末尾写入\n。

write_value/2 获取扁平值列表（假设它是一个仅包含整数和原子的扁平列表）并将其写入文件。