Question

I have a Conversation ActiveRecord model which is essentially the following

class Conversation < ActiveRecord::Base
  has_many :messages, :order => 'created_at ASC'
  belongs_to :latest_message, :class_name => 'Message'
end

I want the latest_message property to always be set to messages.last. I’ve tried the before_save callback but that doesn’t seem to get fired when I add a message like

conversation.messages.create!(
  sender: user,
  body: message_body
)

Any ideas?

Answer 1

Found the answer while I was writing the question up:

  has_many :messages, :order => 'created_at ASC',
           :after_add => :update_latest_message, :after_remove => :update_latest_message

  def update_latest_message(message)
    self.latest_message = self.messages.last
    self.save
  end

ActiveRecord association callbacks let me call a method which updates the message when necessary updated. It would be nice if I didn’t have to call save again…