gistfile1.rb

begin
  $counter = 0
  def update_positions(scope, start)
    scope.each_with_index do |ia, index|
      ia.update_attribute(:position, start + index)
      $counter += 1
    end
  end
  Product.all.each do |p|
    ia = p.image_assignments.where("position IS NOT NULL").order("position DESC").first 
    scope = p.image_assignments.where("position IS NULL")
    if ia
      update_positions(scope, ia.position + 1)
    else
      update_positions(scope, 0)
    end  
  end

  puts $counter
end;nil