Stanis Trendelenburg wrote:
> 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?
In a word, "yes". It's a limitation of the current implementation; patches
welcome or one of the existing devs will get round to it when we have tuits.
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