STI, HABTM & counter_cache


#1

Hello world…

I have an interesting issue that the online docs aren’t helping me with.

In my app I have 4 models

Item < ActiveRecord
Deal < Item
Product < Item
Category < ActiveRecord

Item has_and_belongs_to_many :categories…

On each category record I’d like to maintain a product_count and
deal_count
to increase performance. This doesn’t appear possible with the current
“counter_cache” declaration.

Anyone have ideas on how to approach this?

In the past I’ve just run an hourly cron task to calculate & update all
records of this type, but I feel this probably isn’t the most efficient
(or
accurate).

Ideas, comments?


#2

On 5/22/06, subimage interactive removed_email_address@domain.invalid wrote:

On each category record I’d like to maintain a product_count and deal_count
to increase performance. This doesn’t appear possible with the current
“counter_cache” declaration.

Anyone have ideas on how to approach this?

I don’t know how heavy the updating or saving of the model data is,
but you can always use callbacks to do the counts before saving…

class Category < ActiveRecord::Base
def before_save
self.products_count = Product.count(‘id’, :conditions =>
[“category_id=?”,self.id])
self.deals_count = Deal.count(‘id’, :conditions =>
[“category_id=?”,self.id])
end
end


Sincerely,

Frodo L.


#3

That’s not even where the updating will happen. This would work in a
lazy
fashion, but I was just looking to see if I overlooked anything in AR
that
would do it for me.

Currently I have a cron script that runs (just to make sure the numbers
are
right), plus my own add/remove category methods on Item that update the
counts manually.


#4

Figured out a nice way to handle this for those of you who search it out
later.

There are 2 methods you can call on HABTM relationships “after_add” and
“after_remove”. I’m calling update_counts from there.