このメソッドを使用してincludes
、関連付けを熱心にロードします。
ガイドからの例
Category.includes(:posts => [{:comments => :guest}, :tags]).find(1)
あなたが言ったことに基づいて、それは次のようになります:
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. -----\n\n"
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) -----\n\n"
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
これは恐ろしいデメテルの法則違反です。構造や名前に関係なく、これらのいずれかが変更された場合は、このコードを修正する必要があります。多くの抽象化を導入せずにそれをどのように処理するかはよくわかりません。
本に関しては、たくさんありますが、正直なところ、Railsの世界は、ActiveRecordの最良のプラクティスを構成するものをまだ理解していないと思います(実際、ほとんどすべてのActiveRecordのプラクティスはひどいものだと考えるコミュニティの大部分があります-私は主にそのキャンプにいます)。
しかし、負荷の関連付けを熱心に行うために使用するという上記のようなものが必要な場合は#includes
、ガイドはそのような情報を見つけるのに最適な場所です。私もこのブログとビデオを本当に楽しんだ。