[CDBI] ChildOf

Kate Yoak kate at longmedia.com
Sat Sep 10 01:09:35 BST 2005


> This sounds useful, but I don't quite understand from your
> description how it
> differs from a has_a relationship from the child to the parent
> (other than it
> allows you to specify the accessor name for the parent). What am
> I missing?
>
> I implement similar parent/child relationships like so:
>
> Parent->columns('Primary' => qw/parent_id/);
> Parent->has_many(children => Child);
> Child->columns('Primary' => qw/child_id/);
> Child->columns('Others => qw/parent_id/);
> Child->has_a(parent_id => Parent);
>
> How does ChildOf simplify or improve on this?
>
> Thanks,
> Ed
>

Good point.  Forgot to explain.  The problem with has_a is that it takes
your primary column, your object id (that you are probably using everywhere
in urls, keys, etc) and turns it into a parent object.  That's not very nice
from two perspectives:

#1.  I like my id where it is!  :-)  I mean, really - when I say <a
href="/?a_id=<%$link->link_id%>"> I expect a number to show up. (I believe
it actually will - because of stringify - but read on).

#2.  I don't want to go to the database for the parent just because I am
accessing the child's id.

OK.  So #1 actually works as-is.  Unless you have a custom stringify, your
$link->link_id in a string context should show up as a number.  but it does
so by first going to the database , and then converting the result into the
number (the #2 issue).  What's worse is - I may choose to override
stringify - and break a completely independent module - that's not so good.

All that said, has_a certainly has a place.  It is what gave me the idea,
and I used it heavily to figure out how to make my code work.

I am looking forward to any disagreements to the arguments above.  I am very
new to cdbi (shame on me) and may miss something important.






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