Many-to-Many with just on table plus linking table

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I decided to finally look into Class::DBI, and I'm already quite lost.  The
documentation is a bit spotty and chaotically mixes low-level and high-level
bits.  I'll happily offer some patches, but first I need to figure out what's
going on myself.  (The wiki did not offer clarification on this matter)

I have a table of data.  I have a second table that lists relationships
between items in the first table.

For example, the data table may hold 10 items.  The relationship table
may list:
1 2
1 3
1 4
5 6
5 7
5 8

(both columns refer to the same primary key of the data table)

Following the Actor/Film/Role example from the docs, I tried:

package Forum::DBI;
use base 'Class::DBI::SQLite';
use DBI;

Forum::DBI->connection('dbi:SQLite:dbname=/var/db/site.db', '', '');

#########################################
package Forum::Topic;
use base 'Forum::DBI';

Forum::Topic->table('forum_relations');
Forum::Topic->columns(Primary => qw/message topic/);
Forum::Topic->has_a(message => 'Forum::Message');
Forum::Topic->has_a(topic => 'Forum::Message');

#########################################

package Forum::Message;
use base 'Forum::DBI';

Forum::Message->table('forum_posts');
Forum::Message->columns(All => qw(id title body));
Forum::Message->has_many(messages => [Forum::Topic => 'message']);
Forum::Message->has_many(topics => [Forum::Topic => 'topic']);

And the code:

my $topic = Knight::Forum::Message->create({title => 'Topic 1', body => 'Foo'});
my $message = Knight::Forum::Message->create({title => 'msg 1', body => 'Bar'});
$message->add_to_topics({
	topic => $topic,
});

But I get:
Can't create Forum::Topic object with null primary key columns () at /usr/local/share/perl/5.8.4/Class/DBI/Relationship/HasMany.pm line 89

It turns out that add_to_topics() wants a 'message' value passed, and
add_to_messages wants a 'topic' value passed, with the result of switching the
meanings of my columns.  If I try to be explicit and list both values, it
ignores what I passed.

add_to_* is only barely defined in the documentation, so I've been unsuccessful
in determing what I've done wrong.  Given that the code runs if I meet the
expectations, that makes it out to be a logical error on my part, but I can't
see how my sample is significantly different from the Film/Actor/Role example
in the docs.  

What am I missing?

Thanks in advance.
        -- 
        SwiftOne  /  Brett Sanger
swiftone@xxxxxxxx.xxx