??Best way to subclass BerkeleyDB

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

I want to add some of my own functions to a BerkeleyDB object. i.e. use 'connect' to include all my favorite configurations to initialize a BerkeleyDB and some other functions to some specific data sources. i.e.

    my $db_obj = MyApp::BerkeleyDB->connect("dbname.db");
    ....
    # then I can use BerkeleyDB internal methods
    $db_obj->db_put('key', 'value');
    ....
    # use my own functions..
    $db_obj->myfunc("src", ...);
    ....
[download]

I guess subclassing is the best way to do this. but I am not an OO-guy so far, and not sure how to handle it. trying $class->SUPER is not working. (Apparently, I dont know how to subclass yet:(((). Can anyone help me or give me a hint on this issue, many thanks

package Myapp::BerkeleyDB
use warnings;
use strict;

use base 'BerkeleyDB';
use BerkeleyDB;

# the following code apparently not working!!!
sub connect
{
    my ($class, $dbname) = @_;
    return new BerkeleyDB::Btree
               -Filename => $dbname,
               ......
         or undef;
}
[download]

ttg

Comment on ??Best way to subclass BerkeleyDB Select or Download Code

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Re: ??Best way to subclass BerkeleyDB by Corion (Patriarch) on Jul 17, 2008 at 20:01 UTC
Personally, I would avoid inheritance in favor of delegation: `package MyApp::BerkeleyDB; use strict; use BerkeleyDB; use vars '%bdb_defaults'; %bdb_defaults = ( Filename => 'foo', ... ); sub new { my ($class,%args) = @_; my $self = \%args; bless $self, $class }; sub db { $_[0]->{db} }; sub connect { my ($class,%args) = @_; %args = (%bdb_defaults, %args); my $db = BerkeleyDB::Btree->new(%args); $class->new( db => $db ); };` [download]	[reply] [d/l]
Re: ??Best way to subclass BerkeleyDB by Joost (Canon) on Jul 17, 2008 at 20:03 UTC
`return new BerkeleyDB::Btree -Filename => $dbname, ......` [download] That's wrong. The way calling a constructor from a subclass works in perl is to pass on the $class argument to the superclass's constructor, like this: `return $class->SUPER::new( ... )` [download] Which should make sure the final object will be in the $class class (which will contain the actual requested class - IOW your class, or some subclass of that), instead of the BerkelyDB::Btree class (provided its constructor is coded correctly) "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re: ??Best way to subclass BerkeleyDB by moritz (Cardinal) on Jul 17, 2008 at 20:08 UTC
If you work with `BerkeleyDB::Btree` objects, I think you should subclass that, not `BerkeleyDB` itself. Then you'd write something along these lines: `package Myapp::BerkeleyDB use warnings; use strict; use BerkeleyDB; use base 'BerkeleyDB::Btree'; sub connect { my ($class, $dbname) = @_ return $class->SUPER::new( -Filename => $dbname, ... ) }` [download] But note that I'm not familiar with BerkeleyDB, and the code is not tested.	[reply] [d/l] [select]