From list at mindling.com  Mon May  6 18:48:13 2002
From: list at mindling.com (Seb)
Date: Thu Aug  5 00:21:17 2004
Subject: Subclassing Curiosity
Message-ID: <20020506164802.147D.LIST@mindling.com>

I have a curiosity with regard to subclassing DBI. I'm just not sure I
get the principles involved. I've got a module that is a DBI subclass.
In order to subclass DBI as "package Mine", one must also provide
packages Mine::db and Mine::st, because the database and statement
handles used in DBI are their own classes.

My confusion comes in when I put a constructor in my main package, and
try to use DBI methods on its returned object. (DBI has no constructor
method with which to reference a DBI object, per se)

So I have something like this:

#!/usr/bin/perl
package MyDBI;
use DBI;
@ISA = qw(DBI);

sub new {
  my $class = shift;
  my $self = {};
  bless $self, $class;
  return $self;
}

package MyDBI::db;
@ISA = qw(DBI::db);

package MyDBI::st;
@ISA = qw(DBI::st);

# now our main program

package main;

my $obj = new MyDBI;

# $obj is a MyDBI object, with DBI base methods
print '$obj is a: '.(scalar ref $obj)."\n";

my $dbh = $obj->connect('DBI:Pg:dbname=somedb', undef, undef);

# This generates a warning
# $dbh is a DBI::db object, NOT a MyDBI::db object
print '$dbh is a: '.(scalar ref $dbh)."\n";

# On the other hand, if I use the module name, not my object...

my $dbh2 = MyDBI->connect('DBI:Pg:dbname=somedb', undef, undef);

# No error, and $dbh2 is a proper MyDBI::db object
print '$dbh2 is a: '.(scalar ref $dbh2)."\n";

__END__

The output of the above code looks like this:
$obj is a: MyDBI
DBI subclass 'MyDBI=HASH(0x813c1a0)::db' isn't setup, ignored at MyDBI.pl line 26
$dbh is a: DBI::db
$dbh2 is a: MyDBI::db
<disconnect errors snipped>

Why does the first case ($obj->connect) not do what I expect it to,
while the second case (MyDBI->connect) works fine?

Is this just some basic scoping or inheritance thing that I'm not
understanding?

TIA
Sebastian


From kevin at oreilly.com  Tue May  7 17:13:48 2002
From: kevin at oreilly.com (Kevin Bingham)
Date: Thu Aug  5 00:21:17 2004
Subject: Subclassing Curiosity
In-Reply-To: <20020506164802.147D.LIST@mindling.com>
Message-ID: <5.1.0.14.0.20020507151019.00a8c0c8@pop3.west.ora.com>

Hey Sebastian!

Sorry, I don't know the answer to this particular one, though somebody 
kicking around might. Though considering our meager mailing list, who knows 
when you'll get a response. I suggest posting your question to Perl Monks, 
http://www.perlmonks.org/, which is highly touted by our very own Tom 
Anderson (http://tomacorp.com/, We're not a corporation). On Perl Monks you 
should get an answer right quick.

Kudos!
-Kevin

At 04:48 PM 5/6/2002 -0700, Seb wrote:
>I have a curiosity with regard to subclassing DBI. I'm just not sure I
>get the principles involved. I've got a module that is a DBI subclass.
>In order to subclass DBI as "package Mine", one must also provide
>packages Mine::db and Mine::st, because the database and statement
>handles used in DBI are their own classes.
>
>My confusion comes in when I put a constructor in my main package, and
>try to use DBI methods on its returned object. (DBI has no constructor
>method with which to reference a DBI object, per se)
>
>So I have something like this:
>
>#!/usr/bin/perl
>package MyDBI;
>use DBI;
>@ISA = qw(DBI);
>
>sub new {
>   my $class = shift;
>   my $self = {};
>   bless $self, $class;
>   return $self;
>}
>
>package MyDBI::db;
>@ISA = qw(DBI::db);
>
>package MyDBI::st;
>@ISA = qw(DBI::st);
>
># now our main program
>
>package main;
>
>my $obj = new MyDBI;
>
># $obj is a MyDBI object, with DBI base methods
>print '$obj is a: '.(scalar ref $obj)."\n";
>
>my $dbh = $obj->connect('DBI:Pg:dbname=somedb', undef, undef);
>
># This generates a warning
># $dbh is a DBI::db object, NOT a MyDBI::db object
>print '$dbh is a: '.(scalar ref $dbh)."\n";
>
># On the other hand, if I use the module name, not my object...
>
>my $dbh2 = MyDBI->connect('DBI:Pg:dbname=somedb', undef, undef);
>
># No error, and $dbh2 is a proper MyDBI::db object
>print '$dbh2 is a: '.(scalar ref $dbh2)."\n";
>
>__END__
>
>The output of the above code looks like this:
>$obj is a: MyDBI
>DBI subclass 'MyDBI=HASH(0x813c1a0)::db' isn't setup, ignored at MyDBI.pl 
>line 26
>$dbh is a: DBI::db
>$dbh2 is a: MyDBI::db
><disconnect errors snipped>
>
>Why does the first case ($obj->connect) not do what I expect it to,
>while the second case (MyDBI->connect) works fine?
>
>Is this just some basic scoping or inheritance thing that I'm not
>understanding?
>
>TIA
>Sebastian


From schuyler at tridity.org  Tue May  7 17:40:50 2002
From: schuyler at tridity.org (Schuyler D. Erle)
Date: Thu Aug  5 00:21:17 2004
Subject: Subclassing Curiosity
In-Reply-To: <5.1.0.14.0.20020507151019.00a8c0c8@pop3.west.ora.com>
References: <20020506164802.147D.LIST@mindling.com>
	<5.1.0.14.0.20020507151019.00a8c0c8@pop3.west.ora.com>
Message-ID: <20020507154050.134e1136.schuyler@tridity.org>

I hate to say this, but, speaking from experience, subclassing DBI is *very* difficult to get right. I managed to get the inheritance straightened out, but then for reasons not clear to me, the driver I hacked up dumped core when I tried writing to the database. I'd have debugged it but I don't have the time ATM.

The short answer is, and I'm sure you're not going to like this, avoid subclassing DBI if there's another practical solution to your problem. The DBI is really complicated, and IMHO it's not worth the headache. If you're trying to solve a problem that you really feel can't be solved without subclassing DBI, I recommend describing it in greater detail to the list to see what we come up with...

SDE


On Tue, 07 May 2002 15:13:48 -0700, "Kevin Bingham" <kevin@oreilly.com> wrote:

> Hey Sebastian!
> 
> Sorry, I don't know the answer to this particular one, though somebody 
> kicking around might. Though considering our meager mailing list, who knows 
> when you'll get a response. I suggest posting your question to Perl Monks, 
> http://www.perlmonks.org/, which is highly touted by our very own Tom 
> Anderson (http://tomacorp.com/, We're not a corporation). On Perl Monks you 
> should get an answer right quick.
> 
> Kudos!
> -Kevin
> 
> At 04:48 PM 5/6/2002 -0700, Seb wrote:
> >I have a curiosity with regard to subclassing DBI. I'm just not sure I
> >get the principles involved. I've got a module that is a DBI subclass.
> >In order to subclass DBI as "package Mine", one must also provide
> >packages Mine::db and Mine::st, because the database and statement
> >handles used in DBI are their own classes.
> >
> >My confusion comes in when I put a constructor in my main package, and
> >try to use DBI methods on its returned object. (DBI has no constructor
> >method with which to reference a DBI object, per se)
> >
> >So I have something like this:
> >
> >#!/usr/bin/perl
> >package MyDBI;
> >use DBI;
> >@ISA = qw(DBI);
> >
> >sub new {
> >   my $class = shift;
> >   my $self = {};
> >   bless $self, $class;
> >   return $self;
> >}
> >
> >package MyDBI::db;
> >@ISA = qw(DBI::db);
> >
> >package MyDBI::st;
> >@ISA = qw(DBI::st);
> >
> ># now our main program
> >
> >package main;
> >
> >my $obj = new MyDBI;
> >
> ># $obj is a MyDBI object, with DBI base methods
> >print '$obj is a: '.(scalar ref $obj)."\n";
> >
> >my $dbh = $obj->connect('DBI:Pg:dbname=somedb', undef, undef);
> >
> ># This generates a warning
> ># $dbh is a DBI::db object, NOT a MyDBI::db object
> >print '$dbh is a: '.(scalar ref $dbh)."\n";
> >
> ># On the other hand, if I use the module name, not my object...
> >
> >my $dbh2 = MyDBI->connect('DBI:Pg:dbname=somedb', undef, undef);
> >
> ># No error, and $dbh2 is a proper MyDBI::db object
> >print '$dbh2 is a: '.(scalar ref $dbh2)."\n";
> >
> >__END__
> >
> >The output of the above code looks like this:
> >$obj is a: MyDBI
> >DBI subclass 'MyDBI=HASH(0x813c1a0)::db' isn't setup, ignored at MyDBI.pl 
> >line 26
> >$dbh is a: DBI::db
> >$dbh2 is a: MyDBI::db
> ><disconnect errors snipped>
> >
> >Why does the first case ($obj->connect) not do what I expect it to,
> >while the second case (MyDBI->connect) works fine?
> >
> >Is this just some basic scoping or inheritance thing that I'm not
> >understanding?
> >
> >TIA
> >Sebastian

From kevin at oreilly.com  Wed May 29 13:03:50 2002
From: kevin at oreilly.com (Kevin Bingham)
Date: Thu Aug  5 00:21:17 2004
Subject: Perl Mongers Meeting Thursday the 30th
Message-ID: <5.1.0.14.0.20020529110224.01f17ff8@pop3.west.ora.com>

Hola Fellow Perl Mongers!

The last Thursday of the month is just a few days away, and that means it's 
Perl time!

When: Thursday, May 30, 7:30 to 9:00pm. 6:45pm for those of you interested 
in ordering pizza.
Where:
	O'Reilly & Associates
	1005 Gravenstein Hwy North
	Sebastopol, CA 95472

What? Perl of course!

Directions:
http://www.oreilly.com/oreilly/seb_directions.html
http://maps.yahoo.com/py/maps.py?Pyt=Tmap&addr=1005+Gravenstein+Hwy+N&city=Sebastopol&state=CA&zip=95472-2814&country=us

Your Perl Monger Host,
-Kevin

kevin@oreilly.com 


From list at mindling.com  Wed May 29 13:38:03 2002
From: list at mindling.com (Seb)
Date: Thu Aug  5 00:21:17 2004
Subject: Perl Mongers Meeting Thursday the 30th
In-Reply-To: <5.1.0.14.0.20020529110224.01f17ff8@pop3.west.ora.com>
References: <5.1.0.14.0.20020529110224.01f17ff8@pop3.west.ora.com>
Message-ID: <1022697484.2741.12.camel@localhost.localdomain>

On Wed, 2002-05-29 at 11:03, Kevin Bingham wrote:
> Hola Fellow Perl Mongers!
> 
> The last Thursday of the month is just a few days away, and that means it's 
> Perl time!
> 
> When: Thursday, May 30, 7:30 to 9:00pm. 6:45pm for those of you interested 
> in ordering pizza.

Hi all. I know I was one of the "Thursday's are great!" votes last year,
but I'm unfortunately committed most Thursday nights these days. I
wonder if anyone else is having trouble making the Thursday meetings, or
would prefer a different day? If I'm the lone voice, I'll happily suck
up and deal...and do my best to make what meetings I can, but if anyone
else would like to 'second' a day change vote for future meetings, I'm
all ears :)

The best evenings for me in order of preference are: Tuesday, Monday,
Wednesday, and Sunday.

Cheers
-Sebastian



From eric at eisenhart.com  Wed May 29 14:24:14 2002
From: eric at eisenhart.com (Eric Eisenhart)
Date: Thu Aug  5 00:21:17 2004
Subject: Perl Mongers Meeting Thursday the 30th
In-Reply-To: <1022697484.2741.12.camel@localhost.localdomain>
References: <5.1.0.14.0.20020529110224.01f17ff8@pop3.west.ora.com> <1022697484.2741.12.camel@localhost.localdomain>
Message-ID: <20020529192414.GZ13816@atlantic3.devin.com>

On Wed, May 29, 2002 at 11:38:03AM -0700, Seb wrote:
> Hi all. I know I was one of the "Thursday's are great!" votes last year,
> but I'm unfortunately committed most Thursday nights these days. I
> wonder if anyone else is having trouble making the Thursday meetings, or
> would prefer a different day? If I'm the lone voice, I'll happily suck
> up and deal...and do my best to make what meetings I can, but if anyone
> else would like to 'second' a day change vote for future meetings, I'm
> all ears :)

I'll second the motion; I've been busy almost everything Thursday night
since 1996.  (which is a big part of why I'm never at Perl Monger's meetings
despite otherwise being interested)

> The best evenings for me in order of preference are: Tuesday, Monday,
> Wednesday, and Sunday.

Sunday's frequently a bad day for me and likely a bad day for a lot of
folks.

If you are going to reschedule, make sure to look at stuff like
http://www.linuxmafia.com/bale/ to try and avoid conflicting with the
schedule of anything vaguely nearby that somebody might want to go to that
would also be interested in a Perl meeting.  (looking there it looks like
most Mondays and some Wednesdays are unpopular)

I'd suggest the order of preference be Wednesday, Monday, Tuesday, Thursday
if a move away from thursdays was being considered beyond, well, Seb and
myself...  2nd wednesdays are pretty popular, but the third wednesday and
last wednesday of each month are both thoroughly unpopular (and therefore
good choices a user group).

(for those that don't know, I'm a general malcontent, one of the main NBLUG
people and one of the comp.lang.perl.moderated moderators.)
-- 
Eric Eisenhart                                  eric-dot-sig@eisenhart.com
Perl, SQL, Linux and Web            ^           IRC: Freiheit@openprojects
Coder, Sysadmin and geek           /e\                AIM: falsch freiheit
http://eric.eisenhart.com/         ---                       ICQ: 48217244

From kevin at oreilly.com  Wed May 29 16:41:06 2002
From: kevin at oreilly.com (Kevin Bingham)
Date: Thu Aug  5 00:21:17 2004
Subject: Perl Mongers Meeting Thursday the 30th
In-Reply-To: <20020529192414.GZ13816@atlantic3.devin.com>
References: <1022697484.2741.12.camel@localhost.localdomain>
 <5.1.0.14.0.20020529110224.01f17ff8@pop3.west.ora.com>
 <1022697484.2741.12.camel@localhost.localdomain>
Message-ID: <5.1.0.14.0.20020529142859.01f86cd8@pop3.west.ora.com>

Ahh, I wondered why I hadn't seen you at the meetings, Sebastian.

I have no qualms on moving the date of the meeting. I too have something 
else I could be doing on Thursday nights, but I've been giving PM 
priority.  An now that my Wednesday night class is over, I'm available then.

It sounds like 3rd or last Wednesday of every month might work. What do you 
think?

I will also ask the attendees on Thursday night, since I know a few of them 
are not on the list and just show up.

Kudos!
-Kevin

At 12:24 PM 5/29/2002 -0700, Eric Eisenhart wrote:
>On Wed, May 29, 2002 at 11:38:03AM -0700, Seb wrote:
> > Hi all. I know I was one of the "Thursday's are great!" votes last year,
> > but I'm unfortunately committed most Thursday nights these days. I
> > wonder if anyone else is having trouble making the Thursday meetings, or
> > would prefer a different day? If I'm the lone voice, I'll happily suck
> > up and deal...and do my best to make what meetings I can, but if anyone
> > else would like to 'second' a day change vote for future meetings, I'm
> > all ears :)
>
>I'll second the motion; I've been busy almost everything Thursday night
>since 1996.  (which is a big part of why I'm never at Perl Monger's meetings
>despite otherwise being interested)
>
> > The best evenings for me in order of preference are: Tuesday, Monday,
> > Wednesday, and Sunday.
>
>Sunday's frequently a bad day for me and likely a bad day for a lot of
>folks.
>
>If you are going to reschedule, make sure to look at stuff like
>http://www.linuxmafia.com/bale/ to try and avoid conflicting with the
>schedule of anything vaguely nearby that somebody might want to go to that
>would also be interested in a Perl meeting.  (looking there it looks like
>most Mondays and some Wednesdays are unpopular)
>
>I'd suggest the order of preference be Wednesday, Monday, Tuesday, Thursday
>if a move away from thursdays was being considered beyond, well, Seb and
>myself...  2nd wednesdays are pretty popular, but the third wednesday and
>last wednesday of each month are both thoroughly unpopular (and therefore
>good choices a user group).
>
>(for those that don't know, I'm a general malcontent, one of the main NBLUG
>people and one of the comp.lang.perl.moderated moderators.)
>--
>Eric Eisenhart                                  eric-dot-sig@eisenhart.com
>Perl, SQL, Linux and Web            ^           IRC: Freiheit@openprojects
>Coder, Sysadmin and geek           /e\                AIM: falsch freiheit
>http://eric.eisenhart.com/         ---                       ICQ: 48217244