SPUG: wrapping MLDBM to allow prev/next

[Showell30 at aol.com]

# Hello SPUG.  Surely I am reinventing some wheels here.
# Please comment.
#
#  Thanks,
#
#  Steve
#
# see documentation at __END__

package dbsteve;

use DB_File;
use strict;

sub new
{
    # pass in File
    my $class = shift;
    my $self = {};
    my $file =  $self->{File} = shift;

    $self->{Dirty} = 1; 

    my %table;
    tie (%table, 'MLDBM', $self->{File}, O_CREAT|O_RDWR, 0666, 
        $DB_BTREE) or die "Can't open DB.";
    $self->{Table} = \%table;

    _debug($self);

    return bless $self, $class;
}

sub store
{
    my ($self, $key, $value) = @_;
    $self->{Table}{$key} = $value;
    $self->{Dirty} = 1;
    $self->_setindex($key);
}

sub fetch
{
    my ($self, $key) = @_;
    return undef if not exists $self->{Table}{$key};
    $self->_setindex($key);
    return $self->{Table}{$key};
}

sub prev
{
    my ($self) = @_;
    $self->_clean();
    return (undef, undef) if $self->{CurrKey} <= 0;
    my $key = $self->{Keys}[--$self->{CurrKey}];
    return ($key, $self->{Table}{$key});
}

sub next
{
    my ($self) = @_;
    $self->_clean();
    return (undef, undef) if $self->{CurrKey} >= $#{$self->{Keys}};
    my $key = $self->{Keys}[++$self->{CurrKey}];
    return ($key, $self->{Table}{$key});
}

sub _clean
{
    my ($self) = @_;
    return if not $self->{Dirty};

    $self->{Dirty} = 0;
    $self->{Keys} = [keys %{$self->{Table}}];
    $self->{CurrKey} = 0;
}

sub _debug
{
    while (my($key, $data) = each(%{$_[0]->{Table}}))
    {
        print "$key\n", join(":", @$data), "\n";
    }
}

sub _setindex
{
    my ($self, $key) = @_;

    $self->_clean();

    for my $i (0..$#{$self->{Keys}})
    {
        if ($self->{Keys}[$i] eq $key)
        {
            $self->{CurrKey} = $i;
            last;
        }
    }
}

return 1;

__END__


=head1 DESCRIPTION

Here is what I needed in my database:

   1. Ability to store about 3000 records.
   2. Low performance inserts.
   3. High performance searching.
   4. High performance sequential access through the database (with 
      keys ordered).

This package wraps an MLDBM database that 
has a BTREE DB_File for its guts.  It augments the 
MLDBM/DB_File interface by allowing you to do 
previous and next from the middle of the database.

It removes the hash tie interface, partly due to 
non-virtuous laziness, but also partly to improve the 
clarity of the calling code.

Example usage:
   
    my $db = $steve->new("File.txt");

    $db->store($key, $value);

    $value = $db->fetch($key);
    # undef means not found 

    ($key, $value) = $db->next();
    ($key, $value) = $db->prev();

(This has been tested under Win98 only.)

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