My Rails 3 app has 2 models and a third that's join table between them and their has_many relationships. Basically, User and Show are joined by SavedShow, allowing users to save a list of shows:
class Show < ActiveRecord::Base
has_many :saved_shows
has_many :users, :through => :saved_shows
end
class User < ActiveRecord::Base
has_many :saved_shows
has_many :shows, :through => :saved_shows
end
class SavedShow < ActiveRecord::Base
belongs_to :user, :counter_cache => :saved_shows_count
belongs_to :show
end
I've noticed that the counter_cache field (shows_saved_count) gets incremented automatically just fine, but not decremented. The core of the issue seems to be that removing shows from a user's list is done via delete, which does not trigger updating of the counter_cache:
current_user.shows.delete(@show)
However, I can't call the destroy method here, since that not only deleted the User/Show association in SavedShow, but also the Show object itself, which is not what I want.
Is a counter_cache in this kind of scenario not an appropriate use?
There appears to be a discussion about this as a bug back in 2009, and fixes were discussed, but I'm still seeing the issue in the latest Rails 3.0.
I would just write my own custom handling in the model, but there seems to be no after_delete callback that I can hook into (presumably this is the reason decrementing doesn't work in the first place). Right now, there's only one place in my own code where a delete of the association could occur, so I'll just manually make a call to update the counter, but this seems like like such a fundamental shortcoming or bug of ActiceRecord associations with counter_cache, that I'm wondering if I'm not just missing something.
If this is indeed a genuine problem with counter_caches, what would be the best workaround?