44 lines
1.7 KiB
Erlang
44 lines
1.7 KiB
Erlang
%% ``The contents of this file are subject to the Erlang Public License,
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%% Version 1.1, (the "License"); you may not use this file except in
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%% compliance with the License. You should have received a copy of the
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%% Erlang Public License along with this software. If not, it can be
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%% retrieved via the world wide web at http://www.erlang.org/.
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%%
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%% Software distributed under the License is distributed on an "AS IS"
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%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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%% the License for the specific language governing rights and limitations
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%% under the License.
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%%
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%% The Initial Developer of the Original Code is ProcessOne.
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%% Portions created by ProcessOne are Copyright 2006-2012, ProcessOne
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%% All Rights Reserved.''
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-module(p1_mnesia).
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-author('mickael.remond@process-one.net').
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-export([count_records/2]).
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%% Return the number of records matching a given match expression.
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%% This function is intended to be used inside a Mnesia transaction.
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%% The count has been written to use the fewest possible memory by
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%% getting the record by small increment and by using continuation.
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-define(BATCHSIZE, 100).
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count_records(Tab, MatchExpression) ->
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%% the result contains list of [] for each match: We do not need
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%% actual values as we only count the data.
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case mnesia:select(Tab, [{MatchExpression, [], [[]]}], ?BATCHSIZE, read) of
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{Result,Cont} ->
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Count = length(Result),
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count_records_cont(Cont, Count);
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'$end_of_table' ->
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0
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end.
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count_records_cont(Cont, Count) ->
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case mnesia:select(Cont) of
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{Result,Cont} ->
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NewCount = Count + length(Result),
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count_records_cont(Cont, NewCount);
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'$end_of_table' ->
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Count
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end.
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