in reply to Question regarding DB_File

You can look at the BerkeleyDB module documentation; the tied hash implementation is more or less the same as DB_File, except that it gives you full control over the database. Also, you can look at the documentation of the BerkeleyDB API itself, which can give you an idea what it can do.

I don't know what you mean by "display in the order"; it would depend on how you're doing the displaying. Do you mean that keys(%myDB) will return the order of insertion?

If you're interested in the order of insertion, you may want to look at the DB_RECNO type instead. The BTree will order by key value.

Look at Sleepycat's documentation on BerkeleyDB for details on how this all works. And look into using the BerkeleyDB module instead of DB_File if you want finer-grained control over ordering, duplicate keys, locking, etc.

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Re: Re: Question regarding DB_File
by Stamp_Guy (Monk) on Jul 07, 2001 at 01:22 UTC
    I'm going to describe the catalog number system in detail:
    There are several types of catalog numbers:
    • Numbers with no leading or trailing alphabetical characters (ie: 219)
    • Numbers with leading alphabetical characters (ie: C18)
    • Numbers with trailing alphabetical characters (ie: 219a)
    • Numbers with leading and trailing alphabetical characters (ie: C3a)
    • Numbers that are a range of other numbers (ie: 751-751a or 756-765)
    When sorted a list of the following catalog numbers:
    219, C18, 291a, C3a, 756-765, C21/22, 219a, 756, 291, C20, C30

    Should look like this:

      219
    • 219a
    • 291
    • 291a
    • 756
    • 756-765
    • C3a
    • C18
    • C20
    • C21/22
    • C30
    I can't have normal numbers out of order (as an alphabetical sort would do, with 10 coming before 9), nor can I change the catalog numbering system. How is someone supposed to be able to sort a list like that? It's totally beyond me! I'm really doubting it's possible. I would love for someone to prove me wrong!!!

    Stamp_Guy

[reply]
      It is possible to write a sort function that will produce any arbitrary order your heart desires. However, it might be difficult to write, and the resulting program might not be very efficient. A powerful technique is to transform the keys into something that can be sorted alphabetically. This is much easier to think about, and lets you take advantage of the special key-reduction optimizations that are built into the newer versions of DB_File.

      If you know that the catalog numbers never have more than a certain number of digits, you can make them sortable by adding leading zeroes to numbers, like this:

      • 9 -> 009
      • 123a -> 123a
      • C30 -> C030
      • C21/22 -> C021/022
      ...and so on. You can make this transformation with a simple statement like: 
      $key =~ s/(\d+)/sprintf "%03d", $1/eg;

      [download]
      Remember to keep a copy of the original key around so you can show it to your users, and they won't ever have to know what you've done.

      If you don't have a guarantee about how many digits can be in a catalog number, there are clever solutions... You could, for instance, store the number of digits followed by the actual digits themselves.

[reply]
[d/l]
        Thanks! This worked PERFECTLY!
[reply]

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