xmpp.chapril.org-ejabberd/src/p1_mnesia.erl

%%% ====================================================================
%%% ``The contents of this file are subject to the Erlang Public License,
%%% Version 1.1, (the "License"); you may not use this file except in
%%% compliance with the License. You should have received a copy of the
%%% Erlang Public License along with this software. If not, it can be
%%% retrieved via the world wide web at http://www.erlang.org/.
%%%
%%%
%%% Software distributed under the License is distributed on an "AS IS"
%%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%%% the License for the specific language governing rights and limitations
%%% under the License.
%%%
%%%
%%% The Initial Developer of the Original Code is ProcessOne.
%%% Portions created by ProcessOne are Copyright 2006-2013, ProcessOne
%%% All Rights Reserved.''
%%%
%%% This software is copyright 2006-2013, ProcessOne.

-module(p1_mnesia).

-author('mickael.remond@process-one.net').

-export([count_records/2]).

%% Return the number of records matching a given match expression.
%% This function is intended to be used inside a Mnesia transaction.
%% The count has been written to use the fewest possible memory by
%% getting the record by small increment and by using continuation.
-define(BATCHSIZE, 100).

count_records(Tab, MatchExpression) ->
    case mnesia:select(Tab, [{MatchExpression, [], [[]]}],
		       ?BATCHSIZE, read)
	of
      {Result, Cont} ->
	  Count = length(Result),
	  count_records_cont(Cont, Count);
      '$end_of_table' -> 0
    end.

count_records_cont(Cont, Count) ->
    case mnesia:select(Cont) of
      {Result, Cont} ->
	  NewCount = Count + length(Result),
	  count_records_cont(Cont, NewCount);
      '$end_of_table' -> Count
    end.