Lightweight Databases

Multiple Values

Unlike a hash, a B-tree may store more than one value per key
To enable this, use R_DUP:

     my $dup_btree = DB_File::BTREEINFO->new();
     $dup_btree->{flags} = R_DUP;
     tie %hash, 'DB_File', $file, O_CREAT|O_RDWR, 0666, $dup_btree;

     while (<FRUITS>) {
        my ($color, $fruit) = split / /, $_, 2;
        $hash{$color} = $fruit;
     }

Ordinary hash assignment actually stores the new value in addition to the old one
Hash retrieval recovers only the first stored value
But ->seq will recover all the values:

        $k = "red";
        for ($fail = $db->seq($k, $v, R_CURSOR);
             ! $fail && $k eq "red";
             $fail = $db->seq($k, $v, R_NEXT)) {
          print "$k: $v\n";
        }

        red: apple
        red: cherry
        red: strawberry
        red: raspberry