Simple database

erlang-db.erl

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Database base on list set %
% Andrew N. Shalaev         %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-module(db).
-export([start/0, stop/0, read/1, write/2, delete/1]).
-export([init/0]).
 
% process loop
loop(Db) ->
	receive
		{write, From, Key, Value} ->
			NewDb = write_db(Key, Value, Db),
			From ! {ok, NewDb},
			loop(NewDb);
		{read, From, Key} ->
			From ! read_db(Key, Db),
			loop(Db);
		{delete, From, Key} ->
			NewDb = delete_db(Key, Db),
			From ! {ok, NewDb},
			loop(NewDb);
		{stop, From} ->
			From ! {ok, Db};
		_ ->
			loop(Db)
	end.
 
init() ->
	Db = [],
	loop(Db).
 
%%%%%%%%%%%%%%%%%%%%
% Client functions %
%%%%%%%%%%%%%%%%%%%%
 
% start process
start() ->
	register(my_db, spawn(?MODULE, init, [])).
 
% stop process
stop() ->
	my_db ! {stop, self()},
	receive
		{ok, Db} ->
			io:format("~w~n", [Db])
	end.
 
% write to Database
write(Key, Value) ->
	my_db ! {write, self(), Key, Value},
	receive
		{ok, Db} ->
			io:format("~w~n", [Db])
	end.
 
% read from Database
read(Key) ->
	my_db ! {read, self(), Key},
	receive
		{ok, Value} ->
			io:format("~w~n", [Value]);
		{error, _} ->
			io:format("~w~n", [error])
	end.
 
% delete by key
delete(Key) ->
	my_db ! {delete, self(), Key},
	receive
		{ok, Db} ->
			io:format("~w~n", [Db])
	end.
 
 
%%%%%%%%%%%%%%%%%%%%
% Server functions %
%%%%%%%%%%%%%%%%%%%%
 
% Create
% Update
write_db(Key, Value, Db) ->
	case read_db(Key, Db) of
		{error, instance} -> [{Key, Value}|Db];
		{ok, _} -> [{Key, Value}|delete_db(Key, Db)]
	end. 
 
% Read
read_db(_, []) ->
	{error, instance};
read_db(Key, [{Key, Value}|_]) ->
	{ok, Value};
read_db(Key, [_ | T]) ->
	read_db(Key, T).
 
% Delete
delete_db(Key, Db) ->
	delete_acc(Key, Db, []).
 
delete_acc(_, [], L) ->
	L;
delete_acc(Key, [{Key,_}|T], L) ->
	L ++ T;
delete_acc(Key, [H|T], L) ->
	delete_acc(Key, T, L ++ [H]).