Rails ガイド

production:
  database: my_primary_database
  adapter: mysql2
  username: root
  password: <%= ENV['ROOT_PASSWORD'] %>

production:
  primary:
    database: my_primary_database
    username: root
    password: <%= ENV['ROOT_PASSWORD'] %>
    adapter: mysql2
  primary_replica:
    database: my_primary_database
    username: root_readonly
    password: <%= ENV['ROOT_READONLY_PASSWORD'] %>
    adapter: mysql2
    replica: true
  animals:
    database: my_animals_database
    username: animals_root
    password: <%= ENV['ANIMALS_ROOT_PASSWORD'] %>
    adapter: mysql2
    migrations_paths: db/animals_migrate
  animals_replica:
    database: my_animals_database
    username: animals_readonly
    password: <%= ENV['ANIMALS_READONLY_PASSWORD'] %>
    adapter: mysql2
    replica: true

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  connects_to database: { writing: :primary, reading: :primary_replica }
end

class PrimaryApplicationRecord < ActiveRecord::Base
  primary_abstract_class

  connects_to database: { writing: :primary, reading: :primary_replica }
end

class Person < PrimaryApplicationRecord
end

class AnimalsRecord < ApplicationRecord
  self.abstract_class = true

  connects_to database: { writing: :animals, reading: :animals_replica }
end

class Car < AnimalsRecord
  # animalsデータベースに自動的に話しかける
end

config.active_record.writing_role = :default
config.active_record.reading_role = :readonly

$ bin/rails --help
...
db:create                          # Create the database from DATABASE_URL or config/database.yml for the ...
db:create:animals                  # Create animals database for current environment
db:create:primary                  # Create primary database for current environment
db:drop                            # Drop the database from DATABASE_URL or config/database.yml for the cu...
db:drop:animals                    # Drop animals database for current environment
db:drop:primary                    # Drop primary database for current environment
db:migrate                         # Migrate the database (options: VERSION=x, VERBOSE=false, SCOPE=blog)
db:migrate:animals                 # Migrate animals database for current environment
db:migrate:primary                 # Migrate primary database for current environment
db:migrate:status                  # Display status of migrations
db:migrate:status:animals          # Display status of migrations for animals database
db:migrate:status:primary          # Display status of migrations for primary database
db:reset                           # Drop and recreates all databases from their schema for the current environment and loads the seeds
db:reset:animals                   # Drop and recreates the animals database from its schema for the current environment and loads the seeds
db:reset:primary                   # Drop and recreates the primary database from its schema for the current environment and loads the seeds
db:rollback                        # Roll the schema back to the previous version (specify steps w/ STEP=n)
db:rollback:animals                # Rollback animals database for current environment (specify steps w/ STEP=n)
db:rollback:primary                # Rollback primary database for current environment (specify steps w/ STEP=n)
db:schema:dump                     # Create a database schema file (either db/schema.rb or db/structure.sql  ...
db:schema:dump:animals             # Create a database schema file (either db/schema.rb or db/structure.sql  ...
db:schema:dump:primary             # Create a db/schema.rb file that is portable against any DB supported  ...
db:schema:load                     # Load a database schema file (either db/schema.rb or db/structure.sql  ...
db:schema:load:animals             # Load a database schema file (either db/schema.rb or db/structure.sql  ...
db:schema:load:primary             # Load a database schema file (either db/schema.rb or db/structure.sql  ...
db:setup                           # Create all databases, loads all schemas, and initializes with the seed data (use db:reset to also drop all databases first)
db:setup:animals                   # Create the animals database, loads the schema, and initializes with the seed data (use db:reset:animals to also drop the database first)
db:setup:primary                   # Create the primary database, loads the schema, and initializes with the seed data (use db:reset:primary to also drop the database first)
...

production:
  primary:
    database: my_database
    adapter: mysql2
  animals:
    database: my_animals_database
    adapter: mysql2
    database_tasks: false

$ bin/rails generate migration CreateDogs name:string --database animals

$ bin/rails generate scaffold Dog name:string --database animals

class AnimalsRecord < ApplicationRecord
  self.abstract_class = true

  connects_to database: { writing: :animals }
end

class Dog < AnimalsRecord
end

$ bin/rails generate scaffold Dog name:string --database animals --parent Animals::Record

$ bin/rails g active_record:multi_db

Rails.application.configure do
  config.active_record.database_selector = { delay: 2.seconds }
  config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
  config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
end

class MyCookieResolver < ActiveRecord::Middleware::DatabaseSelector::Resolver
  def self.call(request)
    new(request.cookies)
  end

  def initialize(cookies)
    @cookies = cookies
  end

  attr_reader :cookies

  def last_write_timestamp
    self.class.convert_timestamp_to_time(cookies[:last_write])
  end

  def update_last_write_timestamp
    cookies[:last_write] = self.class.convert_time_to_timestamp(Time.now)
  end

  def save(response)
  end
end

config.active_record.database_selector = { delay: 2.seconds }
config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
config.active_record.database_resolver_context = MyCookieResolver

ActiveRecord::Base.connected_to(role: :reading) do
  # このブロック内のコードはすべてreadingロールで接続される
end

ActiveRecord::Base.connected_to(role: :reading, prevent_writes: true) do
  # Railsは読み取りクエリであることをクエリごとに確認する
end

production:
  primary:
    database: my_primary_database
    adapter: mysql2
  primary_replica:
    database: my_primary_database
    adapter: mysql2
    replica: true
  primary_shard_one:
    database: my_primary_shard_one
    adapter: mysql2
    migrations_paths: db/migrate_shards
  primary_shard_one_replica:
    database: my_primary_shard_one
    adapter: mysql2
    replica: true
  primary_shard_two:
    database: my_primary_shard_two
    adapter: mysql2
    migrations_paths: db/migrate_shards
  primary_shard_two_replica:
    database: my_primary_shard_two
    adapter: mysql2
    replica: true

class ApplicationRecord < ActiveRecord::Base
  primary_abstract_class

  connects_to database: { writing: :primary, reading: :primary_replica }
end

class ShardRecord < ApplicationRecord
  self.abstract_class = true

  connects_to shards: {
    shard_one: { writing: :primary_shard_one, reading: :primary_shard_one_replica },
    shard_two: { writing: :primary_shard_two, reading: :primary_shard_two_replica }
  }
end

$ bin/rails g scaffold Dog name:string --database primary_shard_one

ActiveRecord::Base.connected_to(role: :writing, shard: :default) do
  @id = Person.create! # "default"という名前のシャードにレコードを作成する
end

ActiveRecord::Base.connected_to(role: :writing, shard: :shard_one) do
  Person.find(@id) # レコードは見つからない: "default"という名前のシャードに作成されたためレコードが存在しない
end

ActiveRecord::Base.connected_to(role: :reading, shard: :shard_one) do
  Person.first # shard_oneのread replicaでレコードを探索する
end

$ bin/rails g active_record:multi_db

Rails.application.configure do
  config.active_record.shard_selector = { lock: true }
  config.active_record.shard_resolver = ->(request) { Tenant.find_by!(host: request.host).shard }
end

config.active_record.shard_resolver = ->(request) {
  subdomain = request.subdomain
  tenant = Tenant.find_by_subdomain!(subdomain)
  tenant.shard
}

AnimalsRecord.connected_to(role: :reading) do
  Dog.first     # animals_replicaから読み出す
  Person.first  # primaryから読み出す
end

AnimalsRecord.connected_to(role: :reading, shard: :shard_one) do
  # shard_one_replicaから読み出す。shard_one_replicaのコネクションが存在しない場合は
  # ConnectionNotEstablishedエラーが発生する
  Dog.first

  # primaryのライターから読み出す
  Person.first
end

ApplicationRecord.connected_to(role: :reading, shard: :shard_one) do
  Person.first # primary_shard_one_replicaから読み出す
  Dog.first    # animals_primaryから読み出す
end

class Dog < AnimalsRecord
  has_many :treats, through: :humans, disable_joins: true
  has_many :humans

  has_one :home
  has_one :yard, through: :home, disable_joins: true
end

class Home
  belongs_to :dog
  has_one :yard
end

class Yard
  belongs_to :home
end

SELECT "humans"."id" FROM "humans" WHERE "humans"."dog_id" = ?  [["dog_id", 1]]
SELECT "treats".* FROM "treats" WHERE "treats"."human_id" IN (?, ?, ?)  [["human_id", 1], ["human_id", 2], ["human_id", 3]]

SELECT "home"."id" FROM "homes" WHERE "homes"."dog_id" = ? [["dog_id", 1]]
SELECT "yards".* FROM "yards" WHERE "yards"."home_id" = ? [["home_id", 1]]