export data from mnesia to excel

Question

I have the table user

  -record(person, {id, firstname, lastname}).

this table contains this values :

    1  francoi     mocci     
    2  test        tes  

my goal is how can I export this data from mnesia to excel

I know the inverse way meaning transfer data from excel to mnesia

the solution in this case is to converse the excel in csv.file then use this kind of code to parse the csv file :

%%% --- csv parser in Erlang. ------
%%% To help process large csv files without loading them into
%%% memory. Similar to the xml parsing technique of SAX

-module(csv).
-compile(export_all).

parse(FilePath,ForEachLine,Opaque)->
    case file:open(FilePath,[read]) of
        {_,S} ->
            start_parsing(S,ForEachLine,Opaque);
        Error -> Error
    end.

start_parsing(S,ForEachLine,Opaque)->
    Line = io:get_line(S,''),
    case Line of
        eof -> {ok,Opaque};
        "\n" -> start_parsing(S,ForEachLine,Opaque);
        "\r\n" -> start_parsing(S,ForEachLine,Opaque);
        _ -> 
            NewOpaque = ForEachLine(scanner(clean(clean(Line,10),13)),Opaque),
            start_parsing(S,ForEachLine,NewOpaque)
    end.

scan(InitString,Char,[Head|Buffer]) when Head == Char -> 
    {lists:reverse(InitString),Buffer};
scan(InitString,Char,[Head|Buffer]) when Head =/= Char ->
    scan([Head|InitString],Char,Buffer);
scan(X,_,Buffer) when Buffer == [] -> {done,lists:reverse(X)}.
scanner(Text)-> lists:reverse(traverse_text(Text,[])).

%%traverse_text(Text,Buff)->
  %%  case scan("",$,,Text) of
    %%    {done,SomeText}-> [SomeText|Buff];
 %%       {Value,Rem}-> traverse_text(Rem,[Value|Buff])
   %% end.


traverse_text(Text,Buff)->
    case scan("",$;,Text) of
        {done,SomeText}-> [SomeText|Buff];
        {Value,Rem}-> traverse_text(Rem,[Value|Buff])
    end.


clean(Text,Char)-> 
    string:strip(string:strip(Text,right,Char),left,Char).

and this is an example of function to insert data from csv file to mnesia :

test()->

    ForEachLine = fun(Line,Buffer)->
   [Id, Firstname, Lastname] = Line,

                                    %% here insert each line to the table mnesia

                                     Buffer end,


 InitialBuffer = [],




 csv:parse("/home/test/Desktop/testt.csv",ForEachLine,InitialBuffer).

and this example had no problem

I try with this code :

test()->
    F = fun(T) -> mensia:foldl(fun(X,Acc) -> [X|Acc] end, [],T),
{atomic,L} = mnesia:transaction(F),
file:write_file("filename.txt",[io_lib:format("~p\t~p\t~p~n",[F1,F2,F3]) || 
                 #person{id = F1,firstname = F2,lastname = F3} <- L]).

but I have this error :

syntax error before : '.' 

this error is related to this line :

#person{id = F1,firstname = F2,lastname = F3} <- L]).

I try to correct my code with :

test()->
    F = fun(T) -> mensia:foldl(fun(X,Acc) -> [X|Acc] end, [],T),
{atomic,L} = mnesia:transaction(F),
file:write_file("filename.txt",[io_lib:format("~p\t~p\t~p~n",[F1,F2,F3]) || 
                 #person{id = F1,firstname = F2,lastname = F3} <- L])end.

but I have now this error :

variable 'F' is unbound 

this error is related to this line :

{atomic,L} = mnesia:transaction(F),

I solved this problem with :

test()->
      F = fun(T) -> mensia:foldl(fun(X,Acc) -> [X|Acc] end, [],T)end,
{atomic,L} = mnesia:transaction(F),
file:write_file("filename.txt",[io_lib:format("~p\t~p\t~p~n",[F1,F2,F3]) || 
                 #person{id = F1,firstname = F2,lastname = F3} <- L]).

but when I run my function I have this error :

** exception error: no match of right hand side value {aborted,{{badarity,{#Fun<model.20.69991685>,[]}},
                                                                [{mnesia_tm,apply_fun,3},
                                                                 {mnesia_tm,execute_transaction,5},
                                                                 {model,test,0},
                                                                 {erl_eval,do_apply,5},
                                                                 {shell,exprs,6},
                                                                 {shell,eval_exprs,6},
                                                                 {shell,eval_loop,3}]}}
     in function  model:test/0

I try with this code :

test()->
      F = fun() -> mensia:foldl(fun(X,Acc) -> [X|Acc] end, [],person)end,
{atomic,L} = mnesia:transaction(F),
file:write_file("filename.txt",[io_lib:format("~p\t~p\t~p~n",[F1,F2,F3]) || 
                 #person{id = F1,firstname = F2,lastname = F3} <- L]).

but I also have this error :

** exception error: no match of right hand side value {aborted,{undef,[{mensia,foldl,
                                                                               [#Fun<model.21.662230>,[],person]},
                                                                       {mnesia_tm,apply_fun,3},
                                                                       {mnesia_tm,execute_transaction,5},
                                                                       {model,test,0},
                                                                       {erl_eval,do_apply,5},
                                                                       {shell,exprs,6},
                                                                       {shell,eval_exprs,6},
                                                                       {shell,eval_loop,3}]}}
     in function  model:test/0

Answer 1

You can use the foldl function to create a list and then write this list to a file, using any character as separator (space,comma,tab... depending on the content of your records) and last read the text file with Excel, you will have a popup menu that help you to control the way excel interpret the data. I think it is better tu use an intermediate list, because writing to a file directly may be long for a database transaction.

EDIT: Sorry, I didn't test the line... it should work now.

...
F = fun(T) -> mnesia:foldl(fun(X,Acc) -> [X|Acc] end, [],T) end,
{atomic,L} = mnesia:transaction(F(mnesia_table)),
file:write_file("filename.txt",[io_lib:format("~p\t~p~n",[F1,F2]) || 
                 #table_record{field1 = F1,field2 = F2} <- L]),
...

Answer 2

您忘了在第一行end ：

F = fun(T) -> mensia:foldl(fun(X,Acc) -> [X|Acc] end, [],T) end,