Rails 3.1：在单个查询中通过连接表优化many_to_many？

Question

用户有很多曲目，通过收藏夹。收藏夹有一些关于相关轨道的额外每用户元数据，整个事件使用自定义:as_public散列方法作为json blob返回。

即使我使用JOIN访问相关对象，我也会进行数百次非常基本的SELECT track FROM tracks WHERE track.id='1'查询。 我想优化此查找。

users_controller：

def show
  @user = User.find(params[:id])

  respond_to do |format|
    format.html # index.html.erb
    format.json { render json: @user.to_json(:methods => [:favorites_as_public_tracks]) }
  end
end

user.rb

def favorites_as_public_tracks
  favorites.joins(:track).sort_by(&:created_at).map(&:as_public_track)
end

favorite.rb

class Favorite < ActiveRecord::Base
  belongs_to :user
  belongs_to :track

  #Grabs some stuff from Favorite, merging it with the public data from Track
  def as_public_track
    track.public_attributes.merge(public_attributes_for_merging_onto_track)
  end

  # This stuff gets added onto track.to_json and used by javascript
  def public_attributes_for_merging_onto_track
    return {
      :favorite_id  => id,
      :from_service => from_service,
      :favorited_at => created_at,
      :collection_name => "#{collection_name}, #{from_service}"
    }
  end

  def public_attributes
    private_attrs = [:user_id]

    attributes.reject {|key, val| private_attrs.include? key.to_sym }
  end
end

track.rb

  def public_attributes
    private_attrs = [] #[:id]

    attributes.reject {|key, val| private_attrs.include? key.to_sym }
  end

当我将用户的收藏夹作为公共曲目访问时运行的SQL是：

User Load (0.2ms)  SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", "1"]]
  Favorite Load (7.8ms)  SELECT "favorites".* FROM "favorites" INNER JOIN "tracks" ON "tracks"."id" = "favorites"."track_id" WHERE "favorites"."user_id" = 1 ORDER BY "favorites".created_at DESC
  Track Load (1.3ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 1 LIMIT 1
  Track Load (0.5ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 2 LIMIT 1
  Track Load (0.3ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 3 LIMIT 1
  Track Load (0.3ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 4 LIMIT 1
  Track Load (0.5ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 5 LIMIT 1
  Track Load (0.2ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 6 LIMIT 1
  Track Load (0.2ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 7 LIMIT 1
  Track Load (0.2ms)  SELECT "tracks".* FROM "tracks" WHERE "tracks"."id" = 8 LIMIT 1

如何在不使用track.id ='...'查询数百条SELECT轨道的情况下执行此操作？

谢谢！

Answer 1

如果所有实例的列表保持不变，请考虑将其设置为类方法而不是实例方法。看看是否可以将公共属性和私有属性列表作为类方法。否则，要为每个实例构建这些列表，您将获得每条记录的命中。

通常:include :tracks中的find可以修复它，但我认为这不是问题所在。

祝你好运！