parent = Foo.new
child = Foo.new
link = Foo.new

child.parent = parent
link.link_to = parent
link.is_link = true

parent.save
child.save
link.save

puts link.children.length           # Expected to print 1 which it does

link.children.each do |obj|       # Expects only 1 child, but prints 2
  puts obj.id
end

class Foo
  include Mongoid::Document

  has_many              :children, :foreign_key => "parent_id", :class_name => "Foo"
  belongs_to            :parent, :foreign_key => "parent_id", :class_name => "Foo"
  belongs_to            :link_to, :foreign_key => "link_id", :class_name => "Foo"
  has_many              :linked_by, :foreign_key => "link_id", :class_name => "Foo"

  field :is_link, :type => Boolean, :default => false

  def children_with_bar
    self.is_link ? self.link_to.children : self.children_without_bar
  end

  alias_method_chain    :children, :bar
end