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:
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?
Same issues here but on Rails 2.3. Worth noticing that also adding a touch, like:
belongs_to :user, :counter_cache => :saved_shows_count, :touch => true
Won't update counter cache nor the related updated_at field on association.delete(object).
To workaround the issue usually we manipulate the join model, but that also have some drawbacks.
Patch is here: https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2824-patch-has_many-through-doesnt-update-counter_cache-on-join-model-correctly#ticket-2824-18
Faced a related issue in Rails 5 (with self referential counter cache through a join table) and fixed it as below:
class User < ActiveRecord::Base has_many :saved_shows, :counter_cache => :saved_shows_count has_many :shows, :through => :saved_shows end
On a standard has_many through relation :
class Parent < ApplicationRecord has_many :joins, foreign_key: :parent_id, dependent: :destroy, counter_cache: :joins_count has_many :children, through: :joins, source: 'child' ... class Join < ApplicationRecord belongs_to :parent, counter_cache: :joins_count belongs_to :child end
The counter cache has to be specified on both sides, otherwise it won't we decremented on relation deletion