Rails初学者-查询多个表以一次检索大量信息的最佳实践

Question

我是Rails的初学者，为了学习它，我正在构建一个简单的时间跟踪应用程序。我想用许多带有嵌套信息的表中的大量信息填充管理员的仪表板。

查询数据库以请求一家公司的所有数据以查看所有客户、项目、任务、调整和会议记录的仪表板的最佳做法是什么？

以下是数据的结构：

公司有许多客户端（_M）

客户归属公司有许多项目

项目belongs_to客户端有许多任务（_M）

任务belongs_to项目has_many minutes

分钟belongs_to任务

---

这种数据结构可能非常糟糕。我不知道。

数据的示例视图：

动视
--网站重新设计
---开发
----100分钟

我从这个开始，但我很漂亮，但它可能完全倒退（用户属于公司）：

    @clients = Client.find_all_by_company_id(current_user.company_id)
    @clients.each do |client| 
        project = Project.find_all_by_client_id(client.id)
        puts project.name
        project.each do |project|
            task = Task.find_all_by_project_id(project.id)
            puts task.name
        end
    end

我想这个问题也可以被问到：有没有一本好的书或资源可以完全描述Rails ActiveRecord的最佳实践？

Answer 1

使用includes方法急切地加载关联。

指南示例

Category.includes(:posts => [{:comments => :guest}, :tags]).find(1)

根据你所说的，应该是：

require 'active_record'
require 'logger'
# =====  Config  =====
ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'
ActiveRecord::Base.logger = Logger.new $stdout
ActiveSupport::LogSubscriber.colorize_logging = false
# =====  Schema  =====
ActiveRecord::Schema.define do
  self.verbose = false
  create_table :clients do |t|
    t.string  :name
    t.integer :company_id
  end
  create_table :companies do |t|
    t.string :name
  end
  create_table :projects do |t|
    t.string  :name
    t.integer :client_id
  end
  create_table :tasks do |t|
    t.string  :name
    t.integer :project_id
  end
  create_table :minutes do |t|
    t.integer :quantity
    t.integer :task_id
  end
end
# =====  Classes  =====
class Company < ActiveRecord::Base
  has_many :clients
end
class Client < ActiveRecord::Base
  belongs_to :company
  has_many   :projects
end
class Project < ActiveRecord::Base
  belongs_to :client
  has_many   :tasks
end
class Task < ActiveRecord::Base
  belongs_to :project
  has_many   :minutes
end
class Minute < ActiveRecord::Base
  belongs_to :task
end
# =====  Data  =====
Company.create! name: 'Activision' do |company|
  company.clients.build name: 'Robert Kotick' do |client|
    client.projects.build name: 'Website Redesign' do |project|
      project.tasks.build name: 'Development' do |task|
        task.minutes.build quantity: 100
      end
    end
  end
end
# =====  Querying and displaying  =====
company = Company.find_by_name 'Activision'
clients = Client.includes(projects: {tasks: :minutes}).where(company_id: company.id)
print "n----- The query makes four requests, regardless of how much data you have. -----nn"
clients.inspect # do this to force loading since AR queries are lazy
print "n----- some representation of the data (notice no queries while iterating through) -----nn"
clients.each do |client|
  puts client.name
  client.projects.each do |project|
    puts "-- #{project.name}"
    project.tasks.each do |task|
      puts "--- #{task.name}"
      task.minutes.each do |minute|
        puts "---- #{minute.quantity}"
      end
    end
  end
end
# =====  Output =====
# >> D, [2012-09-12T00:01:42.755414 #72855] DEBUG -- :    (0.7ms)  select sqlite_version(*)
# >> D, [2012-09-12T00:01:42.755890 #72855] DEBUG -- :    (0.2ms)  CREATE TABLE "clients" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255), "company_id" integer) 
# >> D, [2012-09-12T00:01:42.756327 #72855] DEBUG -- :    (0.1ms)  CREATE TABLE "companies" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255)) 
# >> D, [2012-09-12T00:01:42.756728 #72855] DEBUG -- :    (0.1ms)  CREATE TABLE "projects" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255), "client_id" integer) 
# >> D, [2012-09-12T00:01:42.757122 #72855] DEBUG -- :    (0.1ms)  CREATE TABLE "tasks" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255), "project_id" integer) 
# >> D, [2012-09-12T00:01:42.757531 #72855] DEBUG -- :    (0.1ms)  CREATE TABLE "minutes" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "quantity" integer, "task_id" integer) 
# >> D, [2012-09-12T00:01:42.906877 #72855] DEBUG -- :    (0.0ms)  begin transaction
# >> D, [2012-09-12T00:01:42.909242 #72855] DEBUG -- :   SQL (0.5ms)  INSERT INTO "companies" ("name") VALUES (?)  [["name", "Activision"]]
# >> D, [2012-09-12T00:01:42.934937 #72855] DEBUG -- :   SQL (24.7ms)  INSERT INTO "clients" ("company_id", "name") VALUES (?, ?)  [["company_id", 1], ["name", "Robert Kotick"]]
# >> D, [2012-09-12T00:01:42.936110 #72855] DEBUG -- :   SQL (0.1ms)  INSERT INTO "projects" ("client_id", "name") VALUES (?, ?)  [["client_id", 1], ["name", "Website Redesign"]]
# >> D, [2012-09-12T00:01:42.937001 #72855] DEBUG -- :   SQL (0.1ms)  INSERT INTO "tasks" ("name", "project_id") VALUES (?, ?)  [["name", "Development"], ["project_id", 1]]
# >> D, [2012-09-12T00:01:42.937767 #72855] DEBUG -- :   SQL (0.1ms)  INSERT INTO "minutes" ("quantity", "task_id") VALUES (?, ?)  [["quantity", 100], ["task_id", 1]]
# >> D, [2012-09-12T00:01:42.938005 #72855] DEBUG -- :    (0.0ms)  commit transaction
# >> D, [2012-09-12T00:01:42.939882 #72855] DEBUG -- :   Company Load (0.1ms)  SELECT "companies".* FROM "companies" WHERE "companies"."name" = 'Activision' LIMIT 1
# >> 
# >> ----- The query makes four requests, regardless of how much data you have. -----
# >> 
# >> D, [2012-09-12T00:01:42.940458 #72855] DEBUG -- :   Client Load (0.1ms)  SELECT "clients".* FROM "clients" WHERE "clients"."company_id" = 1
# >> D, [2012-09-12T00:01:42.943272 #72855] DEBUG -- :   Project Load (0.1ms)  SELECT "projects".* FROM "projects" WHERE "projects"."client_id" IN (1)
# >> D, [2012-09-12T00:01:42.943919 #72855] DEBUG -- :   Task Load (0.1ms)  SELECT "tasks".* FROM "tasks" WHERE "tasks"."project_id" IN (1)
# >> D, [2012-09-12T00:01:42.944520 #72855] DEBUG -- :   Minute Load (0.1ms)  SELECT "minutes".* FROM "minutes" WHERE "minutes"."task_id" IN (1)
# >> 
# >> ----- some representation of the data (notice no queries while iterating through) -----
# >> 
# >> Robert Kotick
# >> -- Website Redesign
# >> --- Development
# >> ---- 100

这是一个可怕的违反德米特定律的行为，如果这些东西在任何时候发生变化，无论是在结构还是命名上，我们都必须来修复这个代码。如果不引入大量抽象概念，我真的不知道该如何处理。

关于一本书，已经有很多了，但我真的不认为Rails世界还没有弄清楚什么是最好的ActiveRecord实践（事实上，社区中有很大一部分人认为几乎所有的ActiveRecord做法都很糟糕——我主要是在这个阵营中）。

但是，如果你想要像上面这样的东西，即使用#includes来急切地加载关联，那么指南是一个查找此类信息的好地方。我也非常喜欢这个博客和视频。

Answer 2

这会产生与相同的结果

@clients = current_user.company.clients
@clients.each do |client| 
    projects = client.projects
    # puts project.name # makes no sense here
    projects.each do |project|
        project.tasks.each do |task|
            puts task.name
        end
    end
end

Answer 3

尝试类似的东西

 Client.includes(
                      :company =>{:projects=>:tasks})

以上所有内容都应该连接（通过has_one、has_many、belong_to）希望这能有所帮助！