discourse/app/models/concerns/positionable.rb

# frozen_string_literal: true

module Positionable
  extend ActiveSupport::Concern

  included { before_save { self.position ||= self.class.count } }

  def move_to(position_arg)
    position = [[position_arg, 0].max, self.class.count - 1].min

    if self.position.nil? || position > (self.position)
      DB.exec "
      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
      DB.exec "
      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

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

    self.position = position
  end
end