many_to_many_patterns.rb

class BelongsToClass
  # accessors and whatnot
  @@all = []
  def initialize(has_many_class_a_obj, has_many_class_b_obj)
    @has_many_class_a_obj = has_many_class_a_obj
    @has_many_class_b_obj = has_many_class_b_obj
  end
  def self.all
    @@all
  end
end

class HasManyClassA
# ...initializations and whatnot
  def all_belongs_to_objects 
    BelongsToClass.all.select do |belongs_to_obj|
      belongs_to_obj.has_many_a_obj == self 
    end
  end 
  
  def all_has_many_class_b_objects
    self.all_belongs_to_objects.map do |belongs_to_obj|
      belongs_to_obj.has_many_b_obj
    end
  end
end

class HasManyClassB
  # reverse the _a_'s for _b_'s from above to get this class
end