On 1 Feb 2007, at 07:23, Dami Laurent ((PJ)) wrote:
-----Message d'origine-----
De : Matt S Trout [mailto:[EMAIL PROTECTED]
Envoyé : jeudi, 25. janvier 2007 11:59
À : [email protected]
Objet : Re: [Dbix-class] plat-form contest starting soon
Which reminds me, you and I still need to sit down and chat
about synergies.
I reckon I could re-implement the documented interface of
DBIx::DataModel atop DBIx::Class in ~3 days and it would
actually be quite natural to do so, so I'm more and more
suspecting the differences between the projects are largely
in terms of how we conceptualise the interface rather than
how we actually see the underlying domain.
Okay, now that plat-forms is over, let's start investigating some
architectural points. For the discussion I will assume a database
schema similar to the one in DBIx::Class::Manual::Example. In
DBIx::DataModel, this would be written more or less as
# Create a schema class
DBIx::DataModel->Schema('Music');
# Create table classes
# Perl_class DB_table Primary_key
# ---------- -------- -----------
Music->Table(qw/Artist artist artist_id /);
Music->Table(qw/Cd cd cd_id /);
Music->Table(qw/Track track track_id /);
# Declare UML associations
# Class role_name multiplicity
# ----- --------- ------------
Music->Association([qw/Artist artist 1 /],
[qw/Cd cds * /]);
Music->Composition([qw/Cd cd 1 /],
[qw/Track tracks 1..* /]);
Now if I want information about all recent cds and tracks of some
artist, I could write
my $rows = $someArtist->selectFromRoles(qw/cds tracks/)
->(-columns => [EMAIL PROTECTED],
-where => {year => {">" => 2004}},
-orderBy => 'year');
The equivalent SQL is
SELECT @some_column_list FROM cd INNER JOIN track ON
cd.cd_id=track.cd_id
WHERE artist_id = $someArtist->{artist_id}
AND year > 2004
ORDER BY year
my $rs = $artist->search_related('cds',
{ year => { '>' => 2004 } },
{ join => 'tracks', columns => [EMAIL PROTECTED], order_by => 'year',
result_class => $class }
);
(see below for discussion of auto-generating $class)
and each row returned by that query will be blessed into a new class
Music::AutoView::Cd_INNER_Track, created on the fly (if not already
there),
and which inherits from both classes Cd and Track. Multiple
inheritance
makes sense here because a row from that result set contains data
from both
tables (Cd and Track).
Now I have two questions :
1) would such an idea (creating classes on the fly and using
multiple inheritance) be compatible with the architecture of
DBIx::Class ? beneficial ? disastrous ?
Well, in the example you give above I'd most likely just search
across to cds, prefetch back and call $obj->cd->$attr.
However, for more complex virtual views (e.g. cd + track + count
(times track listened to)) I've always been thinking about creating
classes on the fly - the resultset just calls
$rs->result_class->inflate_result
and doesn't care what's in there; I've used on-the-fly classes and
objects for that before now and DBIx::Class really doesn't care. As
for multiple inheritance, the entire package is built on it, so sure,
not a problem :)
I think you'd probably hook search_rs or the attr resolution process
to generate classes on the fly, though I kinda wonder if you mightn't
be better with some sort of AUTOLOAD hack than MI ... probably
depends on the use case.
2) as far as I understand, DBIx::Class also manipulates the
namespace dynamically (loading classes and methods). Did you ever
get in trouble when serializing/deserializing such classes through
Catalyst sessions, as it just happened to me with DBIx::DataModel ?
And if so, how did you solve it ?
So long as the class names are regular it's not really a -major-
problem, you just have to provide Storable hooks. Our big problem is
reconnecting to the $schema, which we still don't have a perfect
solution to.
--
Matt S Trout, Technical Director, Shadowcat Systems Ltd.
Offering custom development, consultancy and support contracts for
Catalyst,
DBIx::Class and BAST. Contact mst (at) shadowcatsystems.co.uk for
details.
+ Help us build a better perl ORM: http://dbix-
class.shadowcatsystems.co.uk/ +
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