discourse/lib/concern/positionable.rb

module Concern
  module Positionable
    extend ActiveSupport::Concern

    def move_to(position_arg)

      position = [[position_arg, 0].max, self.class.count - 1].min

      if self.position.nil? or position > self.position
        self.exec_sql "
        UPDATE #{self.class.table_name}
        SET position = position - 1
        WHERE position > :current_position and position <= :new_position",
        {current_position: self.position, new_position: position}
      elsif position < self.position
        self.exec_sql "
        UPDATE #{self.class.table_name}
        SET position = position + 1
        WHERE position >= :new_position and position < :current_position",
        {current_position: self.position, new_position: position}
      else
        # Not moving to a new position
        return
      end

      self.exec_sql "
      UPDATE #{self.class.table_name}
      SET position = :position
      WHERE id = :id", {id: id, position: position}
    end

    def use_default_position
      self.exec_sql "
      UPDATE #{self.class.table_name}
      SET POSITION = null
      WHERE id = :id", {id: id}
    end
  end
end