HMT collection_singular_ids= deletion of join models is direct, no destroy callbacks are triggered

Question

Just ran into an issue with a has_many :through association and after/before-destroy callbacks not being triggered.

Say, I have users, groups, and an intermediate relati

Answer 1

adding dependent: :destroy to the has many relationship actually calls the before_destroy and after_destroy methods in the Membership class.

class User < ActiveRecord::Base
  has_many :groups, through: :memberships, dependent: :destroy
end

Answer 2

I've struggled with the same problem recently and solved it by extending association and overriding its delete method:

class User < ActiveRecord::Base
  has_many :memberships
  has_many :groups, :through => :memberships do
    def delete(*args)
      groups = args.flatten
      # destroy memberships in order to trigger their callbacks:
      proxy_association.owner.memberships.where(group_id: groups).destroy_all
      super
    end
  end
  ...
end

Answer 3

After carefully examining the API docs, it turns out has_many and has_and_belongs_to_many ("HABTM") have a few options just for this case:

• before_add
• after_add
• before_remove
• after_remove

---

class User < ActiveRecord::Base
  has_many :groups, :through => :memberships, :after_remove => :your_custom_method
end

Judging by how many responses I got, this must not be a very well documented/used feature.

Just noting it here for myself and others who may stumble like I did.