gistfile1.hrl

-module(matrix).
-export([do_this_once/0, update_cell/2, read_cell/2]).

%% index is a tuple: {user_id, article_id}
-record(cell, {index, value = 0 }).

do_this_once() ->
               mnesia:create_schema([node()]),
               mnesia:start(),
               mnesia:create_table(cell,
                              [{attributes, record_info(fields, cell)},
                               {disc_copies, [node()]},
                               {type, set}]).

update_cell(User, Article) ->
                  Cell = #cell{index={User,Article},value=1},
                  F = fun() ->
                    	    mnesia:write(Cell)
		      end,
                  mnesia:transaction(F).

read_cell(User,	Article) ->
		F = fun() ->
		          mnesia:read({cell,{User,Article}})
		    end,
	        mnesia:transaction(F).