ruby-on-rails - 在 Rails 中查询 has_many 关系时不获取 N+1 的智能方法？

Question

我有一个Movie模型和一个MovieStream模型。关系是 Movie has_manyMediaType（和 MediaType belongs_toMovie）。

MediaType 有两个属性“url_broken”（真/假）和“dvd”（真/假）。

在我看来，我有：

Movie.all.includes(:movie_item).each do |movie|
  render partial: 'movie_item'
end

在movie_item-部分我有（简化）：

<h1><%= movie.title %></h1>

<% if movie.media_types.where(:url_broken => false).blank? %>
  No media types exist
<% else %>
<h2>Streams</h2>
<% streams = movie.media_types.where(:dvd => false).each do |media_type| %>
  * <%= media_type.name %>
<% end %>

<h2>Dvd's</h2>
<% dvds = movie.media_types.where(:dvd => true).each do |media_type| %>
  * <%= media_type.name %>
<% end %>

这（显然）会导致 N+1 个查询，但我看不到任何解决方法。是否有可能以某种方式以我可以同时获得streamsand的方式查询视图查询dvds？

喜欢：

Movie.all.join_stream_something.each do |movie, streams, dvds|
render partial: 'movie_item', :locals => { :movie => movie, :streams => streams, :dvds => dvds}
end

没有N+1？结尾

Answer 1

has_many你可以在电影类中定义一个作用域

class Movie < ApplicationRecord
  has_many :valid_url_media_types, -> { where(url_broken: false) }, class_name: "MediaType"
  has_many :not_dvd_media_types, -> { where(dvd: false) }, class_name: "MediaType"
  has_many :dvd_media_types, -> { where(dvd: true) }, class_name: "MediaType"
end

那么在你看来

Movie.all.includes(:valid_url_media_types, :not_dvd_media_types, :dvd_media_types).each do |movie|
  render partial: 'movie_item', movie: movie
end

你的部分：

<h1><%= movie.title %></h1>

<% if movie.valid_url_media_types.blank? %>
  No media types exist
<% else %>
<h2>Streams</h2>
<% streams = movie.not_dvd_media_types.each do |media_type| %>
  * <%= media_type.name %>
<% end %>

<h2>Dvd's</h2>
<% dvds = movie.dvd_media_types.each do |media_type| %>
  * <%= media_type.name %>
<% end %>

Answer 2

看起来你只需要使用.includes

https://apidock.com/rails/ActiveRecord/QueryMethods/includes

Movie.includes(:media_type).all.each do |movie|
  render partial: 'movie_item', :locals => { :movie => movie }
end