positionable.rb

positionable.rb

module Element::Positionable
  extend ActiveSupport::Concern

  included do
    before_create :set_position
    before_update :reposition_before_update

    validates_numericality_of :position, greater_than_or_equal_to: 1, on: :update
  end

  private
    def set_position
      self.position = parent.elements.maximum(:position).to_i + 1
    end

    def reposition_before_update
      move_elements_down_chain if position < position_was
      move_elements_up_chain   if position > position_was
    end

    def move_elements_down_chain
      parent.elements.where('position BETWEEN ? AND ?', position, position_was - 1).update_all('position = position + 1')
    end

    def move_elements_up_chain
      parent.elements.where('position BETWEEN ? AND ?', position_was + 1, position).update_all('position = position - 1')
    end
end