habtm更新问题

Question

我还没有解决这个问题，我有2个型号，播放列表和歌曲 播放列表模型

class PlayList < ActiveRecord::Base
  has_and_belongs_to_many :songs
  #rest of code
end

迁移表

class AddPlayListSong < ActiveRecord::Migration
    def up
  create_table :play_lists_songs, :id => false do |t|
        t.references :play_list, :song
      end
      add_index :play_lists_songs, [:play_list_id, :song_id]
    end

   def down
  drop_table :play_lists_songs
   end
end

我正在尝试将歌曲添加到现有播放列表中（该歌曲已经存在），所以我在更新操作上执行了此操作，这是将歌曲添加到播放列表的表单

我的观点是歌曲/节目中的部分内容

<% @play_lists.each do |play_list| %>
<%=form_for play_list, url: users_play_list_path(play_list.id), method: :put, remote: :true do |f|%>
  <ul>
    <li>
      <%=link_to "", class: "js_update_playlist", id:"play_list" do %>
        <span class="count">(<%=play_list.song_ids.count%>)</span> <%=play_list.name%>
        <%=f.hidden_field :song_ids, :value=>song.id%>
      <%end %> 
    </li>
  </ul>
<%end %> 

  

“js_update_playlist”是一个javascript提交功能 我的控制器

def update

@play_list = current_user.play_lists.find(params[:id])
params[:play_list][:song_ids]
respond_to do |format|
  if @play_list.update_attributes(params[:play_list])
    format.js
  end
end
end

我的问题是，这会删除现有的ID并将其替换为params song_ids，如下所示：

Selector Load (0.9ms)  SELECT "users".* FROM "users" WHERE "users"."type" IN  ('Selector') AND "users"."id" = 1 LIMIT 1
PlayList Load (0.5ms)  SELECT "play_lists".* FROM "play_lists" WHERE "play_lists"."user_id" = 1 AND "play_lists"."id" = $1 LIMIT 1  [["id", "82"]]
(0.2ms)  BEGIN
Song Load (0.5ms)  SELECT "songs".* FROM "songs" WHERE "songs"."id" = $1 LIMIT 1  [["id", 4]]
Song Load (1.5ms)  SELECT "songs".* FROM "songs" INNER JOIN "play_lists_songs" ON "songs"."id" = "play_lists_songs"."song_id" WHERE "play_lists_songs"."play_list_id" = 82
(0.4ms)  DELETE FROM "play_lists_songs" WHERE "play_lists_songs"."play_list_id" = 82  AND "play_lists_songs"."song_id" IN (5)
(0.3ms)  INSERT INTO "play_lists_songs" ("play_list_id", "song_id") VALUES (82, 4)
[paperclip] Saving attachments.
(37.8ms)  COMMIT

我想加载所有play_list的song_ids并将song.id添加到此数组