question.rb

# Please note: this is an oversimplification of the real problem :)

# Say you have this class definition:

class One
  attr_accessor :children

  def initialize data
    puts "Initialize One"
    @children = data.map do |item|
      item = Two.new(item)
    end
  end
end

class Two
  attr_accessor :children

  def initialize data
    puts "Initialize Two"
    @children = data.map { |item| item = Three.new(item) }
  end
end

class Three
  attr_accessor :data

  def initialize data
    puts "Initialize Three"
    @data = data
  end
end

# Now I create a new instance of the One class:
data = [["foo", "bar"], ["foo", "bar"]]
myOne = One.new(data)

# I can now do this:
puts myOne.children.first.children.first.data # "foo"

# Now my question is: how would I access class One methods from class Three?
# i.e: imagine I need to access the @children property of class One from a
# method in class Three. What would be a good way to do that, other than passing
# a 'parent' parameter to every class constructor in the chain?
# 
# Thanks in advance!
# 

It's hard to tell with an abstract example (i.e. without understanding why do you need to call One from Three), but if the relation between the classes is naturally hierarchical (e.g. Series -> Seasons -> Episodes), passing a reference back to the parent object might be a fine solution.

I have Document -> Pages -> Layers, so I guess that counts as "naturally hierarchical". I actually started doing the "pass a reference back to the parent" part, but then I thought that maybe Ruby already had something like object.parent and didn't feel like reinventing the wheel.

Thanks a lot : )

"passing a reference back to the parent object might be a fine solution."

Yes, but this can also be fixed by following the design patterns more closely.

Seems 2 and 3 are models (containing data), where he want to add some logic to 3 that's doing more than related to his model, that should be moved to a controller class.

A controller class should known the structs of the models and be able to make all links, anyway, as quick solution, passing a reference is a fine solution indeed.

In which case does a Layer need to know on what Page he is on?