Re: Constructing objects in multiple CDBI classes w. single SELECT

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> > My question is: could this feature be added to
> > Class::DBI::Relationship::HasMany, or should I make a new kind of
> > relationship?  Or is there a better way to accomplish this?
>
> What you're talking about is caching, and it's fairly tricky to get
> right for multi-process environments.  I would say it's safe enough to
> cache them for the length of a single web request, but caching them for
> the life of the object may not work for people using Class::DBI in a
> long-running script, or with volatile data.  I think anything like this
> should be optional.

Yeah, the caching issue (in general) is a biggie.  But I'm not proposing
that HasMany cache its results - only that it use the pre-constructed
results if they are available.

You can already do:

     my $cd = Music::CD->construct({
         cdid     => 7,
         artist   => 3,
         title    => 'Mule Variations',
         year     => '1999',
     });

I'm suggesting that you also be able to do:

     my $cd = Music::CD->construct({
         cdid     => 7,
         artist   => 3,
         title    => 'Mule Variations',
         year     => '1999',
         tracks   => \@list_of_tracks;
     });

One challenge here would be to discard the cached value of 'tracks'
whenever the $cd object reloads the rest of its columns.


> > If I'm going to create a generalized query mechanism, how can I figure
> > out how the classes are related to each other?  For instance, how can I
> > know that the relationship between Music::Artist and Music::CD is
> > HasMany?
>
> There is class data that will tell you this.  Look at the
> Class::DBI::Relationship::* source code.

Ah - thanks!  It looks like I can do this:

    use Data::Dumper;

    # HasMany
    print "Artist __hasa_list: \n", Dumper(Music::Artist->__hasa_list), "\n";
    print "CD     __hasa_list: \n", Dumper(Music::CD->__hasa_list),     "\n";
    print "Track  __hasa_list: \n", Dumper(Music::Track->__hasa_list),  "\n";

    # HasA
    print "Artist __hasa_rels: \n", Dumper(Music::Artist->__hasa_rels), "\n";
    print "CD     __hasa_rels: \n", Dumper(Music::CD->__hasa_rels),     "\n";
    print "Track  __hasa_rels: \n", Dumper(Music::Track->__hasa_rels),  "\n";


Thanks for the feedback!


Michael


--
Michael Graham <magog@xxxxxxxx.xxx>