mysql - Rails MySQL 查询单表继承 N+1 问题

Question

我正在尝试查找在给定时间段内注册 ActionMovie 计划的所有用户。我遇到了 N+1 问题，我花了很长时间才获得新注册的数量。我想知道是否可以使用 arel_tables 或类似的东西做一些有创意的事情来帮助减少这个过程？

我当前的代码类似于以下内容:

#find all UserMovies created during time frame
user_movies = UserMovie.where(:created_at => start_time..end_time)
#find users
users = user_movies.collect {|um| um.user}
#iterate through each users user_movies and see if the their first action movie was during the time frame I am looking for
users.each do |user| 
  user_movies_array = user.user_movies.map {|um| {um.movie.type => um.created_at}}
  user_movies_array.each do |um|
    if um["ActionMovie"] > start_time
      puts "new user"
    end
  end
end


Class User
  has_many :user_movies
  has_many :movies, :through => :user_movies
end

Class Movie
  has_many :user_movies, :foreign_key => :movie_id
  has_many :users, :through => :user_movies
end

Class UserMovie
   belongs_to :user
   belongs_to :movie
end

Class ActionMovie < Movies
end

Class SuspenseMovie < Movies
end

Answer 1

您是否尝试过使用 :include 选项预先加载 Movie 关联？

看看API docs #has_many 查看具体实现，并滚动到顶部名为关联的预加载的部分以查看总体概述。