stage update

app/controllers/stages_controller.rb

@@ -40,12 +40,9 @@ class StagesController < ApplicationController
     ActiveRecord::Base.transaction do
       begin
         @stage.update_attributes!(stage_params)
+        @stage.stage_shixuns.destroy_all
         unless params[:shixun_id].blank?
-          new_shixun_ids = params[:shixun_id] - @stage.stage_shixuns.pluck(:shixun_id)
-          delete_shixun_ids = @stage.stage_shixuns.pluck(:shixun_id) - params[:shixun_id]
-          @stage.stage_shixuns.where(shixun_id: delete_shixun_ids).destroy_all
-
-          new_shixun_ids.each do |shixun_id|
+          params[:shixun_id].each do |shixun_id|
             shixun = Shixun.where(id: shixun_id).first
             @stage.stage_shixuns.create!(subject_id: @subject.id, shixun_id: shixun.id, position: @stage.stage_shixuns.count + 1) if shixun.present?
           end