Lightweight Databases

Filters

We could use a serialization module like Storable
- It will convert arbitrary values to strings, and back:

        use Storable;
        $hash{numbers} = freeze [1, 4, 2, 8, 5, 7];

        $aref = thaw $hash{numbers};
        print "@$aref\n";

        1 4 2 8 5 7

This is kind of a pain
DB_File will do it automatically:

        my $db = tied %hash;
        $db->filter_store_value(sub { $_ = Storable::freeze($_) });
        $db->filter_fetch_value(sub { $_ = Storable::thaw($_) });

Now this works:

        $hash{numbers} = [1, 4, 2, 8, 5, 7];
        $aref = $hash{numbers};
        print "@$aref\n";

freeze and thaw are called automatically
- Note that the filters use $_ for input and output
Similarly, filter_store_key and filter_fetch_key