Ruby on Rails：迭代關系或關聯的最佳方式

Question

我看到.where語句使用大量的CACHE用戶加載消息而不是關聯來提出如此多的請求。 這是真的嗎？

在這種情況下，我得到一個ActiveRecord_Relation：

@dogs = Dog.where(user_id: current_user.id).order('created_at DESC')

在另一個案例中，我得到一個ActiveRecord_Associations_CollectionProxy：

@dogs = current_user.dogs.order('created_at DESC')

當我在視圖中迭代

<% @dogs.each do |dog| %>
<div><%= dog.name %></div>
<% end %>

我在控制台日志中收到不同的消息：

ActiveRecord_Relation：

User Load (0.3ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
  CACHE User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]

ActiveRecord_Associations_CollectionProxy：

User Load (0.3ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 15], ["LIMIT", 1]]
Dog Load (0.6ms)  SELECT "dogs".* FROM "dogs" WHERE "dogs"."user_id" = ? ORDER BY "dogs"."created_at" DESC  [["user_id", 15]]

哪個更好？ 非常感謝你。

Answer 1

看起來在兩種情況下都應該只調用一次current_user 。 據推測， current_user方法有如下實現：

def current_user
  # read some cookies or something
  User.find_by([...])
end

我不清楚為什么在“ActiveRecord_Relation”版本中會多次調用User.find_by ，但這似乎一定是正在發生的事情。 Rails正在緩存此查詢的結果，因此每次第一次點擊熱緩存后都是如此。

為了排除這一點，您可以memoize的 #current_user 。 這應該防止在第一次調用current_user之后每次看到查詢的Active Record。