Re: How to avoid $class->new($value) with inflate

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--On March 3, 2005 1:18:06 PM +0100 Matija Grabnar 
<matija.grabnar@xxxxx.xx> wrote:

> I have this in my class definition:
> use Date::Manip;
>
> __PACKAGE__->has_a(changed=>'Date::Manip',
>            inflate=>sub {UnixDate(ParseDate(shift),"%e")},
>            deflate=>sub {UnixDate(ParseDate("epoch ".(shift)),
>                       "%Y%m%d%H%M%S")});
> The problem is, Date::Manip doesn't support a routine called 'new', so I
> get
> this error:
> after_set_changed trigger error: Can't locate object method "new" via
> package "Date::Manip" at /usr/share/perl5/Class/DBI/Relationship/HasA.pm
> line 46.
>  at import.pl line 124
>         Class::DBI::_croak('MRTGT::Collection=HASH(0x8b738fc)',
> 'after_set_changed trigger error: Can\'t locate object method ...',
> 'err', '') called at /usr/share/perl5/Class/DBI.pm line 878
>
> "changed" (the field I'm trying to inflate/deflate) is in no way a
> primary key - it's just a data key in the table.
>
> I guess part of my proble is that I don't actualy need a class there -
> the object is a string when deflated, and an integer
> when inflated. But I can't work out how to tell that to has_a...

Your problem here is in the nature of has_a; the notion that the "target" 
attribute is an object is central, so it keeps trying to inflate it to an 
object.  That's deliberate: it lets you chain a custom inflate method with 
the target class's constructor to create the new object.

If you just want to transform a value into a different (non-object) form, 
you can use triggers directly.

I've seen this come up a few times in the last several weeks; maybe it's 
worth writing a small Class::DBI::Relationship::Transform that'd simplify 
the process.  I'll have a crack at it if there's general consensus that 
it'd be a Good Thing.  Any alternate ideas about the name?

--
Regards,
Charles Bailey  < bailey _at_ newman _dot_ upenn _dot_ edu >
Newman Center at the University of Pennsylvania