Erlang Programming/Using ets

ETS local data storage

ETS is the Erlang table storage system, which provides hash-based data storage and access functions. These functions run in constant time. ETS data is stored in a process as long as it is running.

Here is an example of how to use some simple functions in ETS. Notice that the table is not square because goofy has no last name.

Sample program: test_ets.erl

-module(test_ets).
-compile(export_all).

start() -> start( mouse ).

start( Animal ) ->
	Kingdom = ets:new( 'magic',  [] ),
	% note: table is not square
	populate( Kingdom, [{micky,mouse}, {mini,mouse}, {goofy}] ),
	Member = ets:member( Kingdom, micky ),
	io:format( " member ~w ~n ", [ Member ] ),
	%% show_next_key( Kingdom, micky ),
        %% Not work as expected in OTP 19.2
        %% Do a minor change
        FirstKey = ets:first(Kingdom),
        show_next_key(Kingdom, FirstKey),
	find_animal( Kingdom, Animal ).
	
show_next_key( _Kingdom, '$end_of_table' ) -> done;
show_next_key( Kingdom,  Key) ->
	Next = ets:next( Kingdom, Key ),
	io:format( " next ~w ~n ", [ Next ] ),
	show_next_key( Kingdom, Next ).

populate( _Kingdom, [] ) -> {done,start};
populate( Kingdom, [H | T] ) ->
		ets:insert( Kingdom, H ),
		populate( Kingdom, T ).
	
find_animal( Kingdom, Animal ) ->
	ets:match( Kingdom, { '$1', Animal } ).

% ==============
% sample output
% ==============
% 53> test_ets:start().
% member true 
%  next mini 
%  next goofy 
%  next '$end_of_table' 
%  [[mini],[micky]]