How to get the entered values of nested attributes in parent model

App model has many association to links model

App Model

class App < ActiveRecord::Base
  has_many :links, class_name: "Link"
  accepts_nested_attributes_for :links
  before_save :update_flags

  def update_flags
    if self.links.ios_enabled?
      self.flags = "-DFLAG"
    end
  end
end

Link Model

class Link < ActiveRecord::Base
  belongs_to :app
end

When the ios_enabled checkbox is selected, the condition which i used in before_save callback returns the old value of "ios_enabled" attribute from the nested model "Links"

Example: old value = false new value = true

it returns the old value(false) when this condition "self.links.ios_enabled?" is used, not the entered value(true).

How to handle this.Kindly help