DBIx::Recordset::DBSeq - Sequence generator in DBI database

DBIx-Recordset documentation Contained in the DBIx-Recordset distribution.

Index

Code Index:

NAME

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DBIx::Recordset::DBSeq - Sequence generator in DBI database

SYNOPSIS

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 use DBIx::Recordset::DBSeq ;

 $self = DBIx::Recordset::DBSeq ($dbh, 'sequences', $min, $max) ;

 $val1 = $self -> NextVal ('foo') ;
 $val2 = $self -> NextVal ('foo') ;
 $val3 = $self -> NextVal ('bar') ;

DESCRIPTION

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DBIx::Recordset::FileSeq generates unique numbers. State is kept in the one table of a database accessable via DBI. With the new constructor you give an open database handle and sepcify the the table where state should be kept. Optionaly you can give a min and a max values, which will be used for new sequences.

With NextVal you can get the next value for the sequence of the given name.

The table must created in the following form:

create table ( name varchar (32), cnt integer, maxcnt integer, primary key name ) ;

If the sequence value reaches the maxcnt value, NextVal will die with an error message. If maxcnt contains null there is no limit.

AUTHOR

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G.Richter (richter@dev.ecos.de)

SEE ALSO

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DBIx-Recordset documentation Contained in the DBIx-Recordset distribution. 
###################################################################################
#
#   DBIx::Recordset - Copyright (c) 1997-2000 Gerald Richter / ECOS
#
#   You may distribute under the terms of either the GNU General Public
#   License or the Artistic License, as specified in the Perl README file.
#
#   THIS IS BETA SOFTWARE!
#
#   THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
#   IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
#   WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
#
#   $Id: DBSeq.pm,v 1.5 2000/06/26 05:16:18 richter Exp $
#
###################################################################################


package DBIx::Recordset::DBSeq ;

use strict 'vars' ;



## ----------------------------------------------------------------------------
##
## new
##
## creates a new DBIx::Recordset::DBSeq object. 
##
## $dbh          = Database handle
## $table        = table where to keep sequences
##

sub new

    {
    my ($class, $dbh, $table, $min, $max) = @_ ;
    


    my $self = {
                '*Debug'      => $DBIx::Recordset::Debug,
                '*dbh'        => $dbh,
                '*table'      => $table,
                '*DefaultMin' => $min || 1,
                '*DefaultMax' => $max || 'NULL',
               } ;

    bless ($self, $class) ;

    return $self ;
    }



## ----------------------------------------------------------------------------
##
## NextVal
##
## get next value from counter
##
## in   $name = counter name
##


sub NextVal 

    {
    my ($self, $name) = @_ ;

    my $dbh = $self -> {'*dbh'} ;
    
    $dbh -> do ("lock table $self->{'*table'} write") or die "Cannot lock $self->{'*table'} ($DBI::errstr)" ;



    my $sth = $dbh -> prepare ("select cnt,maxcnt from $self->{'*table'} where name=?") or die "Cannot prepare select for $self->{'*table'} ($DBI::errstr)" ;

    $sth -> execute ($name) ;

    my $row = $sth -> fetchrow_arrayref ;
    my $cnt ;
    my $max ;
    
    if (!$row)
        {
        $cnt = $self->{'*DefaultMin'} ;
        $max = $self->{'*DefaultMax'} ;
        my $cnt1 = $cnt + 1 ;
        $dbh -> do ("insert into $self->{'*table'} (name,cnt,maxcnt) values ('$name',$cnt1,$max)") or die "Cannot insert $self->{'*table'} ($DBI::errstr)" ;
        }
    else
        {
        $cnt = $row -> [0] ;
        die "Max count reached for sequence $name" if (defined ($row->[1]) && $cnt+1 > $row->[1]) ;
        $dbh -> do ("update $self->{'*table'} set cnt=cnt+1 where name='$name'") or die "Cannot update $self->{'*table'} ($DBI::errstr)" ;
        }

    $dbh -> do ("unlock table") or die "Cannot unlock $self->{'*table'} ($DBI::errstr)" ;
    
    return $cnt ;
    }

1;

__END__