Question

I want to do some operations on a relation if it has been eager laded (e.g. via includes). In concret terms, I have a data structure Thread which contains n Messages. I want to create a tree of the messages when they’re eager loaded. I tried it as follows:

class Thread
  has_many :messages

  after_initialize do
    gen_tree if messages.loaded?
  end
end

My Problem is that the hook is executed before the the relations have been loaded. Same with after_find.

Is there a way to achieve what I want?

Greetings,
CK

Answer 1

One solution I found is renaming the existing relation method and implement your own:

class Thread
  has_many :messages

  alias_method :messages_orig, :messages
  def messages
    ret = messages_orig

    unless @generated
      @generated = true
      gen_tree
      sort_tree
    end

    ret
  end
end

As far as I tested it, it has no negative side effects.

LG,
CK