Ruby meetup ROM

Me
Nikita Shilnikov
• github.com/ﬂash-gordon
• Whatever developer
• dry-rb and rom-rb core team member

ROM
disinterring the stewardess

ROM vs AR
user = Users.create(name: 'John Doe')
user.age = 30
user.save

ROM vs AR
builder = SqlBuilder.new <<-SQL
UPDATE topic_users tu
SET notification_level =
CASE WHEN should_track THEN :tracking
WHEN should_watch THEN :watching
ELSE notification_level
END,
notifications_reason_id =
CASE WHEN should_track THEN null
WHEN should_watch THEN :auto_watch_category
ELSE notifications_reason_id
END
FROM (
SELECT tu1.topic_id,
tu1.user_id,
CASE WHEN
cu.user_id IS NULL AND tu1.notification_level = :watching AND tu1.notifications_reason_id = :auto_watch_category THEN true
ELSE false
END should_track,
CASE WHEN
cu.user_id IS NOT NULL AND tu1.notification_level in (:regular, :tracking) THEN true
ELSE false
END should_watch
FROM topic_users tu1
JOIN topics t ON t.id = tu1.topic_id
LEFT JOIN category_users cu ON cu.category_id = t.category_id AND cu.user_id = tu1.user_id AND cu.notification_level = :watching
/*where2*/
) as X
/*where*/
SQL

ROM vs AR
--builder = SqlBuilder.new <<-SQL
UPDATE topic_users tu
SET notification_level =
CASE WHEN should_track THEN :tracking
WHEN should_watch THEN :watching
ELSE notification_level
END,
notifications_reason_id =
CASE WHEN should_track THEN null
WHEN should_watch THEN :auto_watch_category
ELSE notifications_reason_id
END
FROM (
SELECT tu1.topic_id,
tu1.user_id,
CASE WHEN
cu.user_id IS NULL AND tu1.notification_level = :watching AND tu1.notifications_reason_id = :auto_watch_category THEN true
ELSE false
END should_track,
CASE WHEN
cu.user_id IS NOT NULL AND tu1.notification_level in (:regular, :tracking) THEN true
ELSE false
END should_watch
FROM topic_users tu1
JOIN topics t ON t.id = tu1.topic_id
LEFT JOIN category_users cu ON cu.category_id = t.category_id AND cu.user_id = tu1.user_id AND cu.notification_level = :watching
/*where2*/
) as X
/*where*/
SQL

Ac#veRecord is not your Domain Layer

Ideology
• No global state
• Immutability
• Explicitness
• Leverage your database
• CQRS

Gems
• rom – core facili-es
• rom-sql – RDBMS interac-on
• rom-repository – applica-on-level interface

Rela%on
• Reads data
• Adapter-speciﬁc

Rela%ons
class Users < ROM::Relation[:sql]
schema(infer: true)
end

Rela%on
schema do
attribute :id, Types::Serial
attribute :name, Types::String
end
end

Rela%on
schema(infer: true)
def by_name(name)
where(name: name)
end
end

Command
• Writes data
• Bound to rela0on

Command
class CreateUser < ROM::Commands::Create[:sql]
relation :users
register_as :create
result :one
end

Container !
rela%ons + commands + DB connec%ons

Container !
rom = ROM.container(:sql, 'sqlite::memory')

Repository
• Accesses applica+on data
• Receives a container

Repository
(ROM::Repository::Root.instance_methods - Object.new.methods).size # => 12
(ROM::Repository::Root.methods - Class.new.methods).size # => 9

Repository
(ApplicationRecord.instance_methods - Object.new.methods).size
(ApplicationRecord.methods - Class.new.methods).size

Repository
(ApplicationRecord.instance_methods - Object.new.methods).size # => 244
(ApplicationRecord.methods - Class.new.methods).size # => 467
TOTAL # => 711

Repository
class UserRepo < ROM::Repository[:users]
end

Repository
def list
users.order(:name).to_a
end
end

Repository
repo = UserRepo.new(rom)
repo.list # => [#<ROM::Struct[User] id=1 name="Jane">]

Changeset
changeset = repo.changeset(name: 'John')
changeset.map(:add_timestamps).to_h
# => {:name=>"John",
# :created_at=>2017-03-18 16:33:19 +0300,
# :updated_at=>2017-03-18 16:33:19 +0300}
repo.create(changeset.map(:add_timestamps))

Changeset
changeset = repo.changeset(user.id, name: 'John Doe')
changeset.diff? # => true
changeset.diff # => {:name=>'John Doe'}

Many containers
rom = ROM.container(:sql, DB_URL)
rom_replica = ROM.container(:sql, DB_REPLICA_URL)
read_only_repo = UserRepo.new(rom_replica)

Many adapters
rom = ROM.container(
default: [:sql, 'postgres://localhost/rom_repository'],
cache: [:sql, 'sqlite::memory']
) do |c|
c.gateways[:cache].create_table :counters do
primary_key :id
column :user_id, Integer
column :type, String
column :value, Integer
end
end

Many adapters
) do |c|
primary_key :id
end
c.relation(:users) do
schema(infer: true)
end
end

Many adapters
) do |c|
primary_key :id
end
c.relation(:users) do
schema(infer: true)
end
c.relation(:counters) do
gateway :cache
schema(infer: true)
def for_users(users)
where(user_id: users.pluck(:id))
end
end
end

Many adapters
relations :counters
end

Many adapters
repo.
users.
combine(many: {
counters: [repo.counters.for_users, id: :user_id]
}).
where { id <= 2 }.
to_a
=begin
[
#<ROM::Struct[User] id=1 name="Jane" counters=[
#<ROM::Struct[Counter] id=1 user_id=1 type="posts" value=3>,
#<ROM::Struct[Counter] id=2 user_id=1 type="comments" value=512>
]>,
#<ROM::Struct[User] id=2 name="Joe" counters=[]>
]
=end

No N+1!
I, [2017-03-18T19:37:14 #6638] (0.000765s) SELECT "id", "name" FROM "users" WHERE ("id" <= 2) ORDER BY "users"."id"
I, [2017-03-18T19:37:14 #6638] (0.000172s) SELECT ìd`, ùser_id`, `type`, `value` FROM `counters` WHERE (ùser_id` IN (1, 2)) ORDER BY `counters`.ìd`

One database
repo.aggregate(:counters).where { id <= 2 }.to_a

Moar backends
• rom-yaml
• rom-h*p
• rom-mongo
• rom-couchdb
• rom-ka3a
• rom-redis
• rom-git

Plans
ROM 4.0 roadmap
• More powerful mapping facili2es
• Cross-adapter associa2ons
• Move a bunch of features from rom-repository to rom-core
• Auto-migra2ons in rom-sql ✨

Help
• Give it a try
• Use diﬀerent adapters
• Docs
• Contribute

Ruby meetup ROM

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