如何在事件发生之前记录Rails查询？

Question

默认情况下，Rails logger会在执行后显示SQL。有时 - 主要是查询需要很长时间 - 我想配置记录器在执行之前输出SQL。然后它可以在数据库响应后添加后续日志。

基本思路是这样的：

10:01:01 POST Load Executing "SELECT * from posts;' 
10:01:03 POST Load 1712ms 

如何Rails的配置，打破SQL日志分为2步这样吗？

Answer 1

在执行之前，没有标准的方式可以配置记录器输出SQL查询。

但是，您仍然可以通过扩展ActiveRecord::LogSubscriber类以这种方式记录查询。现在

# initializers/extensions/active_record_logger.rb 
module Extensions 
    module ActiveRecordLogger 
    IGNORE_PAYLOAD_NAMES = ActiveRecord::LogSubscriber::IGNORE_PAYLOAD_NAMES 

    # ActiveRecord::LogSubscriber doesn't implement this method. 
    # This method will be invoked before event starts processing. 
    # It's exactly we are looking for! 
    def start(name, id, payload) 
     super 

     return unless logger.debug? 
     return if IGNORE_PAYLOAD_NAMES.include?(payload[:name]) 

     name = payload[:name] 
     sql = payload[:sql] 

     name = color(name, nil, true) 
     sql = color(sql, nil, true) 

     debug "STARTING #{name} #{sql}" 
    end 
    end 
end 

ActiveRecord::LogSubscriber.include Extensions::ActiveRecordLogger 

你会得到的查询日志之前执行。例如，查询

User.find 1 

会产生

STARTING User Load SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", 1]] 
#<User id: 1, username: "dimakura", created_at: "2015-09-08 13:16:42", updated_at: "2015-09-08 13:16:42"> 

Answer 2

我认为您正在寻找explain导轨方法。所以，你需要实现类似的东西：

@query = Some.model.query 
Rails.logger @query.explain 
ActiveRecord::Base.silence do 
    @query.load 
end 
Rails.logger "Finished" 

当然，你可以添加定时器，原因，异常处理et.c.