An expensive transaction in acts_as_list

list.rb

# This has the effect of moving all the lower items up one.
def decrement_positions_on_lower_items(position=nil)
  return unless in_list?
  position ||= send(position_column).to_i
  acts_as_list_class.unscoped.update_all(
    "#{position_column} = (#{position_column} - 1)", "#{scope_condition} AND #{position_column} > #{position}"
  )
end