There's no built-in functionality for this, but you can just add
after_create and before_destroy callbacks to increment/decrement the parent
records with the correct count based on any number of conditions.

You can see how it's implemented in the Rails source here:
http://github.com/rails/rails/blob/master/activerecord/lib/active_record/associations.rb#L1451

On Tue, Dec 8, 2009 at 10:28 AM, liquid_rails <[email protected]>wrote:

> I would like for the database to keep a count of postings belonging to
> a specific category (can do that), that are NOT expired (don't know
> how to do that).   Are there any built-in functions to do this?
>
> Thanks!
>
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