[Dbix-class] Result Sets of Joins

[William Reardon]

Marc Mims wrote:
> * William Reardon <wdr1 at pobox.com> [080929 08:40]:
>> Excuse me if this is an obvious question, but I'm still learning the
>> DBIx::Class way & haven't had any luck finding answers...
>>
>> Coming from the common DBI/hand-crafted sql route, I'm used to the world
>> where I could join a many-to-one table and easily access columns from
>> either table in the result.  E.g.:  SELECT author.name, book.title
>> FROM..., getting a hashref of the result, them doing something like:
>>
>> print $row->{name}, " by ", $row->{title}, "\n"
> 
> Something like this should work:
> 
> # example 1
> my $rs = $schema->resultset('Book')->search(
>     {'author.user_id' => 1},
>     {prefetch => 'author'}
> );
> while ( my $book = $rs->next ) {
>     print $book->title, " by ", $book->author->name, "\n";
> }

Ah, so this *didn't* work for me, but it did send me down the right road 
-- I had a simple (stupid!) copy/paste error.  The Book table actually 
had two belongs_to relationships to differnt tables.  In copy/pasting 
the first 'author' relationship, I changed everything but the very 
'author' parameter itself, pointing it to the wrong thing.

After finding & fixing it (and slamming my head against the keyboard), 
everything worked fine.  Much more in line with how I expected. :)

Thanks for your help, Marc.  I really appreciate it.

-Bill

> Is user_id the PK for the author table?  If so, you could do this:
> 
> # example 2
> my $author = $schema->resultset('Author')
>     ->find($user_id, {prefetch => 'books'});
> for my $book ( $author->books ) {
>     print $book->title, " by ", $author->name, "\n";
> }
> 
> I'm assuming that Books has a belongs_to relationship to Author and
> Author has a has_many relationship to Books. By getting a Book resultset
> in example 1, the prefetch of author results in a single object.  In
> example 2, you get a single Author object that includes a Books
> resultset.
> 
> Both examples make a single call to the database.
> 
> 	-Marc
> 
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