[Dbix-class] prefetching and many_to_many

[Stanis Trendelenburg]

Hi List,

I am playing around with the many-to-many relationship example from
DBIx::Class::Manual::Cookbook (user <-> address, via user_address
mapping table). So far everything works as expected.

Now I'm trying to to fetch a user and also prefetch all his addresses.
After some trial and error I found out that this:

  my $user = $user_rs->find( 1,
   { prefetch => { user_address => address } }
  );

produces the correct SQL (via DBIC_TRACE):

  SELECT me.id, me.name, user_address.user, user_address.address,
         address.id, address.street
  FROM user me
  LEFT JOIN user_address user_address ON ( user_address.user = me.id )
  JOIN address address ON ( address.id = user_address.address )
  WHERE ( ( me.id = ? ) ) ORDER BY user_address.user: '1'

Now when I want to access the address objects linke this:

  foreach ( $user->addresses ) { print $_->street };

it prints the correct results, but every row in the address table is
fetched from the database again:

  SELECT address.id, address.street
  FROM user_address me
  JOIN address address ON ( address.id = me.address )
  WHERE ( me.user = ? ): '1'

To actually use the prefetched values, I have to access the related
objects via the mapper object:

  foreach ( $user->user_address ) { print $_->address->street };

(No SQL generated)

What is the difference between the two methods? I find the 1st one
(using the many-to-many accessor) to be more intuitive, but somehow it
does not seem to "know" about the prefetched values?

Thanks,

Stanis