如何使用activiti modeler

Posted 2023-04-30

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了如何使用activiti modeler相关的知识，希望对你有一定的参考价值。

参考技术A Activiti Modeler用于保存BPMN规范相关的对象，例如可用于将这些模型转换为相应的流程图对象：
              // 创建一个BPMN模型实例
           BpmnModel bpmnModel = new BpmnModel();
           // 创建流程
           Process process = new Process();
           process.setId("myProcess");
           bpmnModel.getProcesses().add(process);
           // 创建任务
           UserTask task = new UserTask();
           task.setId("myTask");
           process.addFlowElement(task);
           // 设置任务的图形信息
           GraphicInfo g1 = new GraphicInfo();
           g1.setHeight(100);
           g1.setWidth(200);
           g1.setX(110);
           g1.setY(120);
           bpmnModel.addGraphicInfo("myTask", g1);
           // XML转换器，将BPMN模型转换为XML文档
           BpmnXMLConverter converter = new BpmnXMLConverter();
           System.out.println(new String(converter.convertToXML(bpmnModel)));
参考自《疯狂工作流讲义第2版（Activiti6）》。

Active Model Serializer - 提高渲染性能

【中文标题】Active Model Serializer - 提高渲染性能【英文标题】：Active Model Serializer - Increasing Render Performance 【发布时间】：2017-01-05 19:39:19 【问题描述】：

我遇到了一种特殊情况，即由 ActiveModel::Serializer 生成的渲染 json 非常慢（大约 6-8 秒）。如何提高此渲染的速度？这是代码。

型号：

class Comment < ActiveRecord::Base
  has_many :children_comments,
           class_name: 'Comment',
           foreign_key: 'parent_comment_id'

  belongs_to :user
  belongs_to :parent_comment,
             class_name: 'Comment',
             foreign_key: 'parent_comment_id'
end

序列化器：

class CommentSerializer < ActiveModel::Serializer
  include ActionView::Helpers::DateHelper

  attributes :id, :message, :created_at_in_words,
             :created_at, :parent_comment_id
  belongs_to :user
  has_many :children_comments

  def created_at_in_words
    time_ago_in_words(object.created_at) + ' ago'
  end

  def children_comments
    object.children_comments.map do |comment|
      CommentSerializer.new(comment).as_json
    end
  end
end

class UserSerializer < ActiveModel::Serializer
  attributes :id, :name, :avatar_url

  def avatar_url
    object.avatar.url
  end
end

在我的控制器中

  parent_comments = Comment.where(parent_comment_id: nil)

  render status: :ok,
         json: parent_comments,
         each_serializer: CommentSerializer,
         key_transform: :camel_lower

这是我调用服务器时的部分日志输出。如您所见，Active Model Serializer 进行每个查询调用大约需要 20 毫秒。

Started GET "/comments?lesson_id=420" for ::1 at 2016-09-01 11:09:14 -0400
Processing by Api::CommentsController#index as HTML
  Parameters: "lesson_id"=>"420"
  User Load (0.4ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1  ORDER BY "users"."id" ASC LIMIT 1  [["id", 102]]
  Lesson Load (0.5ms)  SELECT  "lessons".* FROM "lessons" WHERE "lessons"."id" = $1  ORDER BY position ASC LIMIT 1  [["id", 420]]
  Comment Load (53.0ms)  SELECT "comments".* FROM "comments" WHERE "comments"."commentable_id" = $1 AND "comments"."commentable_type" = $2 AND "comments"."parent_comment_id" IS NULL  [["commentable_id", 420], ["commentable_type", "Lesson"]]
[active_model_serializers]   User Load (0.5ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (24.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41401]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41402]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (22.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41403]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (21.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41404]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41405]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41406]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41407]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41408]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41409]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41410]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41411]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41412]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41413]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (23.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41414]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41415]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41416]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (23.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41417]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41418]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41419]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41420]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41421]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.9ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41422]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41423]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41424]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41425]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41426]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41427]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41428]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41429]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41430]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.9ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41431]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41432]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41433]]
[active_model_serializers]   CACHE (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (21.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41434]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41435]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (21.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41436]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41437]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41438]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (22.9ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41439]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41440]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41441]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.9ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41442]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41443]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41444]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41445]]
[active_model_serializers]   CACHE (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41446]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41447]]
[active_model_serializers]   CACHE (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41448]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41449]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.0ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41450]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41451]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41452]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41453]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.0ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41454]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (22.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41455]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (22.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41456]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41457]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41458]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41459]]
[active_model_serializers]   CACHE (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41460]]
[active_model_serializers]   CACHE (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41461]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41462]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41463]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41464]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41465]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41466]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41467]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.5ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41468]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41469]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41470]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.0ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41471]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41472]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41473]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.0ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41474]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41475]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41476]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (19.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41477]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41478]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41479]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.4ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41480]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.2ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41534]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41535]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.6ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41536]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.8ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41537]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (18.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 41538]]
[active_model_serializers] Rendered ActiveModel::Serializer::CollectionSerializer with ActiveModelSerializers::Adapter::Json (3895.33ms)
Completed 200 OK in 4007ms (Views: 1222.1ms | ActiveRecord: 2743.8ms)

根据 Michal 的回答，这里是日志中的一个小样本。

Started GET "/comments?lesson_id=370" for ::1 at 2016-09-02 17:13:06 -0400
Processing by Api::CommentsController#index as HTML
  Parameters: "lesson_id"=>"370"
  User Load (0.4ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1  ORDER BY "users"."id" ASC LIMIT 1  [["id", 102]]
  Lesson Load (0.4ms)  SELECT  "lessons".* FROM "lessons" WHERE "lessons"."id" = $1  ORDER BY position ASC LIMIT 1  [["id", 370]]
  Comment Load (23.0ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" IS NULL AND "comments"."commentable_type" = 'Lesson' AND "comments"."commentable_id" = 370
  User Load (0.9ms)  SELECT "users".* FROM "users" WHERE "users"."id" IN (102)
  Comment Load (25.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" IN (38641, 38687, 38733)
  CACHE (0.0ms)  SELECT "users".* FROM "users" WHERE "users"."id" IN (102)
[active_model_serializers]   Comment Load (20.3ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 38642]]
[active_model_serializers]   User Load (0.5ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (20.7ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 38643]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]
[active_model_serializers]   Comment Load (30.1ms)  SELECT "comments".* FROM "comments" WHERE "comments"."parent_comment_id" = $1  [["parent_comment_id", 38644]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 102]]

我的理论是这样的。我确信 children_cmets 序列化导致了大部分性能问题。因为我必须为每条评论调用 children_cmets，这会导致级联效应。我想知道我是否可以重写代码以提高性能。

【问题讨论】：

你在使用 oj gem 吗？是的，oj gem 在性能上几乎没有差异。您是否尝试对此进行分析？使用 ruby-prof 或 stackprof？它会告诉你哪个部分实际上很慢。 @Michal 不，我没有。但是查看日志输出，我发现序列化程序在进行评论查询时花费的时间最长。我确信这是导致性能缓慢的原因。您可以使用 sql 查询从日志中发布输出吗？ 【参考方案1】：

将您的 ActiveRecord 查询更改为此

parent_comments = Comment.where(parent_comment_id: nil).includes(:user, children_comments: :user)

它将摆脱 N + 1 个查询。

【讨论】：

不幸的是，这并没有改善时间。评论加载时间大致相同。 @jason328 日志输出现在看起来如何？发布在问题中。嗯 @jason328，上面的 ActiveRecord 查询对我来说看起来不错，你一定要检查 N+1 个查询。在重命名关联关系时，您可能需要尝试一下，关于children_comments 的命名（您可能以comments 开头）。【参考方案2】：

您遇到了 n+1 查询类型问题。不幸的是，includes 在这里并没有真正帮助您，因为它只帮助您处理关联的一个级别 - 它避免单独获取***评论的子级，而不是孙子或曾孙。

您可以通过维护您自己的用户 id 缓存到用户对象来优化用户查找（rails 缓存缓存原始数据，但会一遍又一遍地重新实例化对象），但要使这显着更快，您需要更改加载 cmets 的方式。

如果您使用支持它的数据库（例如 postgresql），则可以选择递归查询（请参阅 https://hashrocket.com/blog/posts/recursive-sql-in-activerecord 以获取工作示例）。我不知道这会随着树越来越深而扩展。

如果递归查询不是一个选项，那么有几种方法会涉及更改您存储的内容。

一种是物化路径模式。例如，根评论的 id 为 1，子评论的 id 为 101，其中一个子评论的 id 为 426。最后一条评论的路径是 1/101/426。它的所有兄弟姐妹都有以1/101/ 开头的路径。这意味着您可以使用类似查询（末尾带有通配符）来快速查找子树。 ancestry gem 实现了这一点。如果 cmets 被移动，那么您需要重写所有 cmets 子项（和孙子等）的路径，但这可能与您的用例无关。我认为非常深的树是有问题的。

另一个是嵌套集合模式。核心思想是父节点存储其所有子节点及其子节点等的最小和最大 id。这允许一次性检索所有这些子节点。另一方面是插入和更新需要重写大量此类数据（比物化路径更多）。多年来，已经有各种 gem 实现了这一点（目前的一个似乎是 awesome_nested_set）。

还值得检查您是否有正确的索引来支持您的查询 - 除非确实有很多具有给定父级的 cmets，否则 20-30 毫秒对于一个查询来说似乎相当长。

【讨论】：

您已经给出了最全面的答案以及几种可能的解决方案。为此，我要给你信用。感谢您的广泛回答。

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