Re: many2many

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Hi Will--

    Thanks, I got the many2many to work and I agree with you about the 
naming conventions. I was using tables designed by someone else.

    Now that I've got that working, I am back to getting cdbi factory to 
work, but I can't seem to  get it initialized correctly. The code has:

use base 'Class::DBI::Factory';
my $rebase = Class::DBI::Factory->new;
   $rebase->set_db ({db_type => 'mysql',
                 db_name => 'rebase:localhost',
                 db_username => 'barry',
                 db_password => '',
                });
   $rebase->use_classes (qw/Enzyme Site EnzymeSite/);
   print "db_name: " . $rebase->db_name . "\n";

but then I get the output:

Use of uninitialized value in concatenation (.) or string at 
C:\Development\Perl\try\Tisdall\try_many2many.pl line 26.
db_name:

Set_db did not initialize the values for db name,  username and  password 
even thought I used the same values when I used class::bdi->set_db. I also 
tried

db_type => 'dbi:mysql',

in the factory set_db but that didn't help either.

TIA

Barry

----- Original Message ----- 
From: "William Ross" <will@xxxxxxx.xxx>
To: "Barry Dancis" <bdancis@xxxxxxx.xxx>
Cc: "class dbi list" <cdbi-talk@xxxxxx.xxxxx.xxx>
Sent: Monday, April 11, 2005 2:58 PM
Subject: Re: many2many



On 11 Apr 2005, at 17:46, Barry Dancis wrote:

> I am trying to implement a many to many relationship with
>
> #=============================
> {package Sites;
> Sites->has_many (siteenzymes => ['EnzymeSites' => 'enzid']);
>
> #=============================
> {package Enzymes;
> Enzymes->has_many (enzsites => ['EnzymeSites' => 'siteid']);
>
> #=============================
> {package EnzymeSites;
> EnzymeSites->columns(Primary => qw/ siteid enzid /);
> EnzymeSites->has_a (enzid => 'Enzymes');
> EnzymeSites->has_a (siteid => 'Sites');
>
> but when I execute:
>
> my $enzyme = Enzymes->retrieve(enzyme => 'TstI');
> my @sites = $enzyme->enzsites;
> I get the error:
>
> enzymes is not a column of EnzymeSites

The foreign class column name in a has_many relationship defaults to
the moniker of the calling class, on the reasonable assumption that
when a cd has many tracks, the cd of the track will be recorded in a
column called 'cd'. This is in the docs.

If i remember rightly, the moniker of a class defaults to the name of
its data table if no other moniker is declared. I don't think this is
in the docs.

Your Enzymes class is declaring a has_many relationship with
EnzymeSites. The extra [] clause just tells that relationship object to
return a column of the EnzymeSites object rather than returning the
whole object.

The data table for your Enzyme class is called 'enzymes'. By default
the has_many relationship will get that as the moniker and look for a
column with that name in the EnzymeSites class, but the real name of
the column is 'enz_id'. To avoid this trouble, you just have to specify
the column name. To avoid future trouble, I'd specify the class moniker
too:

Enzymes->moniker('enzyme');
Enzymes->has_many(enzsites => ['EnzymeSites' => 'siteid'], 'enzid');
Sites->has_many (siteenzymes => ['EnzymeSites' => 'enzid'], 'siteid');

Personally I also avoid the 'id' suffix on column names: it describes
the contents of the column well enough, but becomes confusing when the
column is inflated. In your case, it leads to statements like:

my $site_id = $enzyme->site_id->siteid;

But that's very much a question of taste, and there are plenty here who
would disagree.

best

Will

ps. Tony, didn't the moniker used to de-pluralise itself? Or did I
imagine that?