[Dbix-class] multiple has_many rels in prefetch not supported in 0.081?

[Moritz Onken]

Am 25.08.2008 um 20:43 schrieb Matt S Trout:

> On Sat, Aug 23, 2008 at 08:53:27AM +0200, Moritz Onken wrote:
>> Something like:
>>
>> my $search = {  };
>> my $attr = { prefetch => [ qw/tracks tags/ ] };
>>
>> my $cd = $schema->resultset("Artist")->first->cds->search($search,
>> $attr)->first;
>> $cd->tracks->all;
>> $cd->tags->all;
>>
>> did work for me. If you say it breaks in many cases I might have not
>> tested it enough.
>> Is there an alternative to get the same data with one query but still
>> have all the relations working?
>
> No, there isn't.
>
> But the point we're trying to make is that all the cases -we- tried,  
> it
> was broken.
>
> So what we need from you is to try and work out what cases you were  
> hitting
> that weren't broken, so we can make the exception only happen in cases
> that are genuinely broken.
>
> The exception was introduced to try and produce a sane error rather  
> than
> a random explosion further down. I'd be very happy to be able to -not-
> throw an exception and have it work, but obviously we also still  
> want to
> throw an exception when we know it's not going to work.
>
> Could you unpatch as Peter showed you and try some experiments, see  
> if you
> can figure out what works and what doesn't - or at least provide a  
> bunch
> of examples that do and don't and we'll try and figure out what the  
> common
> factor is?
>
> -- 

Yes, I'm on it. What I found out is that calls like $cd->tags->all  
return some
rows multiple times. Depending on the rows which are in $cd->tracks- 
 >all and
the order of how you put the relations in the prefetch arrayref.
Therefore ->count doesn't work as well. But I think this could be  
fixed with
some kind of a implementation of distinct in perl (List::MoreUtils uniq)

As I said I'm on it and writing some examples and tests.

moritz