Question

  render :json => {
    "playlist" => playlist_description,
    "songs" => @playlist.songs.as_json(:include => {:playlist_songs => {:only => [:id, :position]}})
  }

上面的代码导致对数据库的1 + N个查询，一个为每首歌加载playlist_songs。播放列表预装在@playlist中。

这太慢了，我该如何优化？

Answer 1

我的猜测：此刻你并不急于加载playlist_songs。您当前正在等待as_json调用 - 之后所有歌曲都已加载 - 然后代码必须遍历每首歌曲然后获取playlist_songs。

我的猜测（这完全未经测试，可能包含错误）

@playlist.songs.all(:include => :playlist_songs).as_json(:include => {:playlist_songs => {:only => [:id, :position]}})

AFAICT，这应该首先急切加载所有歌曲和 playlist_songs ...然后呈现为json。

Answer 2

我强烈建议您使用rabl等JSON构建器进行集成。它将使你的生活更容易前进，并且非常好地分离JSON表示的“视图”。几个月前我做了转换，但没有回头。

在您的控制器中：

@playlist = Playlist.where(:id => params[:id]).includes(:playlist_songs)

然后rabl模板可能是这样的：

object @playlist
attribute :description
child :playlist_songs do
  attributes :id, :position
end

Answer 3

render :json => {
  "playlist" => playlist_description,
  "songs" => @playlist.songs.all.as_json(:include => {:playlist_songs => {:only => [:id, :position]}})
}

^猜猜

Rails：渴望加载as_json包含

3 个答案: