在这种情况下如何急切加载？

Question

class Model RunningTracks < ActiveRecord::Base
  has_many :achievements
  has_many :runners, through: :achievements

class Model Runner < ActiveRecord::Base
  has_many :achievements
  has_many :running_tracks, through: :achievements

class Model Achievement < ActiveRecord::Base
  belongs_to :runner
  belongs_to :running_tracks

在主页上有一个each do 列表来显示所有 RunningTrack。在轨道旁边，我们显示一个按钮，将其标记为运行。急切的加载解决方案是控制器查询中的includes 和references（Rails 4）：

class RunningTracksController
  def index
    @running_tracks = RunningTracks.includes(:achievements).references(:achievements)
  end

为了提高可用性，每条记录旁边的按钮如果已标记，则不应可见。 （将在辅助方法中重构）

@running_tracks.each do |track|
  .
  - unless track.achievements.map(&:user_id).include? current_user.id
    = button_to "done", running_track_mark_as_done_path(track)

这行得通...但是...随着数据库获得更多记录，它将查询很多成就，因此自定义关联和includes 查询仅针对current_user（设计）的成就应该是解决办法。

class Model RunningTracks < ActiveRecord::Base
  .
  has_many :achieved_runns, -> { where user_id: current_user.id }, class_name "Achievement"

但因为 current_user 在模型中不可访问，所以这不起作用。我认为不可能将变量传递给 hay_many 关联，是吗？

是否有更有效的解决方案来预先加载所有 RunningTrack，包括仅当前用户的成就？ 感谢您宝贵的时间！

Answer 1

以下内容很丑陋并且打破了 ActiveRecord 的比喻，但随着数据库的增长，您可以快速查找。也许其他人可以通过一种方法将其保持在急切加载范式中。

class RunningTrack
   # Returns a Set (for fast lookups) of track IDs that have at least one achievement for the provided user
   def self.running_track_ids_for_achievements_for_user(user_id)
      Set.new Achievement.where(:user_id => user_id).pluck(:running_track_id)
   end
end

然后在你的控制器中：

class RunningTracksController
   def index
      @running_tracks = RunningTracks.all
      @running_track_ids_for_achievements_for_user = RunningTrack.running_track_ids_for_achievements_for_user(current_user.id)
   end
end

你的看法：

- unless @running_track_ids_with_achievements_for_user.include? track
   = button_to "done", running_track_mark_as_done_path(track)