after_destroy callback is not triggered in call to collection_singular_id

I have a salesperson model:

class Salesperson < User has_many :dealers_and_salespeople, :class_name => "DealerAndSalesperson"

def dealer=(dealer)

self.dealer_ids = dealer.nil? ? [] : [dealer.id]

end ...

end

The dealer_and_salesperson model is like this:

class DealerAndSalesperson < ActiveRecord::Base set_table_name "dealers_and_salespeople" belongs_to :salesperson belongs_to :dealer

after_create :create_event_22 after_destroy :create_event_24

def create_event_22

Event.create(:event_type_id => 22, :salesperson_id => salesperson_id, :dealer_id => dealer_id)

end

def create_event_24

Event.create(:event_type_id => 24, :salesperson_id => salesperson_id, :dealer_id => dealer_id)

end

end

When I call salesperson.dealer = an_existing_dealer, the after_create callback is triggered. But when I call salesperson.dealer = nil, the after_destroy callback is not triggered at all.

Please let me know if this is by design, or I'm not using rails in the right way.

Thanks, Yi Zhang