Orderable Sortable Has Many without Through

Orderable / Sortable Has Many without Through

There is an existing example for order able has_many :through associations. However, for simpler cases it can be done directly without :through. I have tested the below with Mongoig adapter and using and it worked well. Please feel free to clean up or optimize.

Example below is for a Library model that has many Books association.

  def books_ids=(ids)
    unless (ids = ids.map(&:to_s)) == (current_ids = self.books.map(&:_id).map(&:to_s))
      (current_ids - ids).each { |id| self.books.select{|b|b.id.to_s == id}.first.remove }
      ids.each_with_index.map do |id, index|
        if current_ids.include?(id)
          (book = self.books.select{|b|b.id.to_s == id}.first).position = (index+1)
        else
          b = Book.find(id)
          b.library = self
          b.position = (index+1)
        end
      end
    end
  end