ruby-on-rails - MiniProfiler 列出的额外查询

Question

在我的 Controller 操作中，我 included View 所需的所有关联，以避免多次调用数据库。 (我试图隔离 View 层以仅呈现 Controller 收集的数据)。

I'v found out that the view still communicates with the database (17 Queries):

这些 17 extra queries 不需要。由于我已经从控制台测试了 Controller 查询，并且它成功收集了部分 _dropdown 所需的所有数据。 (在 5 个查询 中)，无需任何进一步的数据库通信。

这是 query在我的 Controller 中，这意味着要避免 N+1问题。 (包括 View 中调用的所有变量)

这是下拉代码:

- @messages.each do |message|
    %li.conversation-container
        %a{href: conversation_path(message.conversation_id)}
            - if message.sender != current_user 
                .notification-avatar{style: "background: url(#{message.sender.avatar_url}); background-size: contain; background-repeat: no-repeat; background-position: 50% 50%;"}
            - else
                - other_participant = message.conversation.conversation_participants.select{|p| p.user_id != current_user.id }.first.user 
                .notification-avatar{style: "background: url(#{other_participant.avatar_url}); background-size: contain; background-repeat: no-repeat; background-position: 50% 50%;"}
            %p
                %strong
                    - if message.sender != current_user 
                        = message.sender.name
                    - else
                        = other_participant.name
                %br
                - if message.sender == current_user
                    %i.fa.fa-mail-reply-all
                = truncate(message.body,length: 25)

                .time
                    = time_ago_in_words(message.created_at)
                    ago
- if @messages.count == 0
    %li
        .empty-state-text-white
            No messages

控制台输出:

2.0.0-p353 :006 > ms = Message.dropdown_for(3).all
  Message Load (1.2ms)  SELECT "messages".* FROM "messages" LEFT JOIN messages AS m ON messages.id != m.id 
 AND m.conversation_id = messages.conversation_id 
 AND messages.created_at < m.created_at INNER JOIN conversation_participants AS cp ON cp.conversation_id = messages.conversation_id AND cp.user_id = 3 WHERE (m.id IS NULL) ORDER BY cp.seen , cp.updated_at DESC LIMIT 5
  User Load (0.7ms)  SELECT "users".* FROM "users" WHERE "users"."id" IN (6, 4, 5)
  Conversation Load (0.4ms)  SELECT "conversations".* FROM "conversations" WHERE "conversations"."id" IN (4, 2, 3)
  ConversationParticipant Load (0.2ms)  SELECT "conversation_participants".* FROM "conversation_participants" WHERE "conversation_participants"."conversation_id" IN (4, 2, 3)
  User Load (0.6ms)  SELECT "users".* FROM "users" WHERE "users"."id" IN (6, 3, 4, 5)
 => [#<Message id: 8, body: "saSasa", sender_id: 6, conversation_id: 4, sent: true, attachment_id: nil, attachment_type: nil, created_at: "2014-11-17 16:05:40", updated_at: "2014-11-17 16:05:40">, #<Message id: 2, body: "asdnas dagsdashjdg jahs d", sender_id: 4, conversation_id: 2, sent: true, attachment_id: nil, attachment_type: nil, created_at: "2014-11-17 11:32:36", updated_at: "2014-11-17 11:32:36">, #<Message id: 6, body: "SADASD A DSA ", sender_id: 5, conversation_id: 3, sent: true, attachment_id: nil, attachment_type: nil, created_at: "2014-11-17 13:43:34", updated_at: "2014-11-17 13:43:34">] 

2.0.0-p353 :007 > ms.first.conversation.conversation_participants.select{|cp| cp.user_id != 3}.first.user
 => #<User id: 6, first_name: "Ddsfsd", middle_name: nil, last_name: "Fsdfsd", photo: nil, email: "1@k.com", encrypted_password: "$2a$10$5sGIb2DbQ1ctMrTzD3AJ0uV18hhiC5Ei1wcfE7MSAvRU...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 1, current_sign_in_at: "2014-11-17 15:27:06", last_sign_in_at: "2014-11-17 15:27:06", current_sign_in_ip: "127.0.0.1", last_sign_in_ip: "127.0.0.1", confirmation_token: nil, confirmed_at: "2014-11-17 15:27:48", confirmation_sent_at: "2014-11-17 15:27:05", unconfirmed_email: nil, failed_attempts: 0, unlock_token: nil, locked_at: nil, authentication_token: nil, created_at: "2014-11-17 15:27:05", updated_at: "2014-11-17 15:27:48", slug: "ddsfsd_fsdfsd"> 

2.0.0-p353 :008 > ms.count
 => 3 

我怎样才能阻止这些查询在没有目的的情况下运行？

Answer 1

* 调试

在调试可能导致此问题的所有可能因素之后。
我试图设置 config.cache_classes对，在我的 development.rb .这成功地删除了所有额外的查询。

我得出的结论是(默认情况下)当类没有被缓存时，不会为任何模型加载架构。换句话说，当 config.cache_classes设置为 false ，每个模型的架构作为单独的查询为每个请求加载。

这是一个类似的问题 column_definitions method being called before and after every single SQL statement on PostgreSQL .

* 结论

cache_classes should be set to false in development environment. Ignore the extra internal queries from postgresql connection adapter loading the schema for each model since it not going to affect your production environment (production has config.cache_classes set to true).