gryphon has asked for the wisdom of the Perl Monks concerning the following question:

Greetings fellow monks,

I'm playing around with Class::DBI again, and I'd really like to pass dynamic DSNs and other database connection information to my parent class from the calling script or application module. I've been using Config::IniFiles for a while now, and I really like it and would like to continue to use it. I've been toying with a few ideas on how to combine my various wants, and here's what I've come up with. 

#!/usr/bin/perl
use strict;
use warnings;
use Config::IniFiles;
my $cfg;
BEGIN {
  $cfg = new Config::IniFiles( -file => 'settings.ini' );
  $ENV{_MyCDBI} = join("\t",
    $cfg->val('Database', 'dsn'),
    $cfg->val('Database', 'Username'),
    $cfg->val('Database', 'Password')
  );
}
use MyCDBI;

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I'm using use here just because it's habit and because it runs parallel to using other CPAN stuff and my own application modules. However, I could just as easily require instead of use to simplify things.

my $cfg = new Config::IniFiles( -file => 'settings.ini' );
$ENV{_MyCDBI} = join("\t",
  $cfg->val('Database', 'dsn'),
  $cfg->val('Database', 'Username'),
  $cfg->val('Database', 'Password')
);
require MyCDBI;

[download]

Either way, I just split the various bits inside my Class::DBI parent. 

package MyCDBI;
use base 'Class::DBI::mysql';
__PACKAGE__->connection(split("\t", $ENV{_MyCDBI}));

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Now, this works just fine, and I'm more or less happy with it for my purposes, but it's far from optimum. First of all, I'm using poor-man's serialization of the bits for the database connection. A better solution would include the capability of sending stuff like {AutoCommit => 1} and whatever else. Plus, the code in the calling script is somewhat obnoxious. I'd love to use use if possible, but even without, it's three lines long. I know if merlyn saw this, he'd cringe and use a one-liner alternative.

So my question is thus: What are some better ways of doing this? (Better = less lines of code, more flexible data sent, more class encapsulation, more coffee, etc.) One thing I was thinking about was writing an abstraction class for my parent Class::DBI class. I've always hated having to refer to the subclass names multiple times.

my $obj = MyCDBI::SomeDBObj->retrieve(1);
# versus
my $cls = new MyCDBI;
my $obj = $cls->SomeDBObj->retrieve(1);

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But I can't really say exactly why I don't like this.

I've been reading about Class::DBI::Factory, but I have to admit that much of it goes way over my head. Should I just grin and deal with the learning curve? Or is there a simpler way?

gryphon
code('Perl') || die;

Replies are listed 'Best First'.
Re: Abstracting Class::DBI Database Connection Data
by hardburn (Abbot) on Jun 08, 2004 at 20:40 UTC

    Read the section of the Class::DBI doc titled "Dynamic Database Connections / db_Main".

    ----
    send money to your kernel via the boot loader.. This and more wisdom available from Markov Hardburn.

[reply]

      Greetings hardburn,

      I have. Many times. But apparently I'm not smart enough to figure it out. This works:

      package MyCDBI;
use base 'Class::DBI::mysql';
__PACKAGE__->connection('dbi:mysql:mydb', 'me', 'mypwd');

      [download]

      But this doesn't:

      package MyCDBI;
use base 'Class::DBI::mysql';
sub db_Main {
  use DBI;
  return DBI->connect('dbi:mysql:mydb', 'me', 'mypwd')
    or die DBI->errstr;
}

      [download]

      I get the nice error message: Can't locate object "fetch_hash" via package "DBI::st" at Class/DBI/mysql.pm line 65. The calling script only uses MyCDBI and prints a hello world, so there's nothing from that that's causing this. Any suggestions?

      gryphon
      code('Perl') || die;

[reply]
[d/l]
[select]

        Doesn't db_Main have to return an Ima::DBI compatible handle now, rather then just a plain DBI handle?

        It says so, rather obliquely:

        The preferred method for doing this is to supply your own db_Main() method rather than calling connection(). This method should return a valid database handle, and should ensure it sets the standard attributes described above, preferably by combining $class->_default_attributes() with your own.

        I think the part about a valid database handle is where they mean one derived from Ima::DBI.

        Update:

        If you scan up right above the Dynamic Database Connections / db_Main heading, it says:

        We use the inherited RootClass of DBIx::ContextualFetch from Ima::DBI, and you should be very careful not to change this unless you know what you're doing!

        Maybe someone with a little more knowledge on this than I can provide a working example?

[reply]

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