[Openinteract-help] Re: Callbacks on links_to?

[Chris W. <ch...@cw...>]

On Dec 19, 2003, at 5:25 PM, Vsevolod (Simon) Ilyushchenko wrote:
 > ...
> So far this worked out well until I started using 'links_to'. Assume 
> that MyPublisher and MyBook are my classes, SPOPS_Publisher and 
> SPOPS_Book are SPOPS classes. Instances of MyPublisher refer to 
> instances of SPOPS_Publisher, instances of MyBooks refer to instances 
> of SPOPS_Books.

Right -- I think it's easier (now) to make MyBooks a subclass of 
SPOPS_Books (more below)

> The expected object behavior is this:
>
> $aMyPublisher->books produces an array of MyBooks.
>
> In actuality,
>
> $aMyPublisher->books produces an array of SPOPS_Books.
>
> Is it possible to generate the desired result without straining the 
> framework too much? Looks like I can achieve this by mucking around in 
> SPOPS::ClassFactory::DBI and providing some kind of callbacks within 
> the get/add/remove functions, but I'd like to get an official word 
> first

Coincidentally, I made a change in 0.80 that allows you to do:

SPOPS class: SPOPS_Books
Your class: MyBooks isa SPOPS_Books
SPOPS class: SPOPS_Publisher
Your class: MyPublisher isa SPOPS_Publisher

Then declare in your publisher configuration:

  links_to => { MyBooks => 'link_table' }

So you can use your subclass ('MyBooks') rather than the 
SPOPS-generated class as the class to link to. I know this goes against 
the GoF declaration to 'Prefer composition over inheritance', but it is 
a much cleaner solution that using the 'code_class' configuration item 
(crazy idea that). I've modified all the code in OpenInteract2 to use 
this pattern, naming the SPOPS-generated classes 'FooPersist' for 
clarity.

The only caveat is that you cannot 'use base' to declare the parent 
relationship; you need to use @ISA explicitly:

   package MyBooks;
   @MyBooks::ISA = qw( SPOPS_Books );

   sub my_custom_sub {
       ...
   }

The change in SPOPS 0.80 to enable this was just to do a 'require' on 
the class specified in has_a and links_to before using it in the code 
generation process.

Hope that makes sense.

Chris

--
Chris Winters
Creating enterprise-capable snack systems since 1988