add_to_ question

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Consider this a cross between curiousity and using a sledge hammer in
a china shop. So forgive me for this is a ramble. :-)

For the sake of this email, let's assume we're talking about
Music::Artist and Music::CD from the SYNOPSIS pod. Let's also assume
that as a developer, I chose to use Class::DBI to make my life easier
[aka lazy], but that I want the consumer of my modules to use My API,
and not rely on the fact that the Class::DBI API may or may not always
be there underneath the covers.

For example, let's take the act of adding a CD to an Artist. I would
rather the consumer rely on my Music::Artist->add instead of
Music::Artist->add_to_cds()

No biggie, we can just create:

	sub Music::Artist::add {
		my ($self, $data) = @_;
		return $self->add_to_cds($data);
	}

Then I simply call:

	my $artist = Music::Artist->create({ artistid => 1, name => 'U2' });

	my $cd = $artist->add({ 
		cdid   => 1,
		title  => 'October',
		year   => 1980
	});


Now, I would also like the consumer to be able to do something like
this (assuming a Music::CD object may be created/stored/passed aruond
elswhere and is used as more than just it's hash storage):

	my $artist = Music::Artist->create({ artistid => 1, name => 'U2' });

	$artist->add($cd);

where ref($cd) eq 'Music::CD', a CD object that has been created
elsewhere/earlier using:

	my $cd = Music::CD->construct({ 
		cdid   => 1,
		title  => 'October',
		year   => 1980,
	})


Obviously, this fails with:

	"add_to_cds needs data" due to HasMany.pm line 82/83:

		return $self->_croak("add_to_$accessor needs data")
			unless ref $data eq "HASH";


Nothing surprising so far as I'm not passing a pure HASH. So, my
questions comes down to what is the lesser of a few evils.

I can copy my Music::CD's hash into a fresh hash, and send that along:

	sub Music::Artist::add {
		my ($self, $data) = @_;

		if (ref $data eq 'Music::CD') {
			my %hash = $data->{};
			return $self->add_to_cds(\$%hash);
		} else {
			return $self->add_to_cds($data);
		};
	}

Or, there is another option. What if the add_to did the following instead?

		return $self->_croak("add_to_$accessor needs data")
			unless UNIVERSAL::isa($data, 'HASH');


What kinds of evils would ensue after that process? I'd file this
partly under DO What I Mean when add_to receives something other than
a hash.


The 3rd option is some ref/bless/reconsicrate magic that I yet don't
understand to make my $cd back into what add_to expects.

Thanks,
-=Chris