This document introduces Scala ActiveRecord, an ORM library for Scala that aims to provide an ActiveRecord-like experience. It summarizes the motivations for creating Scala ActiveRecord, which were to have a more usable database library that supports type-safety, conventions over configuration, and avoids repetition. It describes key features of Scala ActiveRecord like validations, associations, and callbacks. It also provides examples of basic CRUD operations and queries using Scala ActiveRecord's interface.

1. Scala ActiveRecord
The elegant ORM library for Scala

2. Author github.com/y-yoshinoya
主にScalaとRuby on Railsの業務をやってます
Play Framework 2.0 を Beta バージョンから業務で
採用を試みる
DBライブラリにはSqueryl, Anorm, ScalaQuery を
採用
Scala ActiveRecord はより使えるDBライブラリを求
めた結果の産物

3. 概要
Summary

4. Scala ActiveRecord
https://github.com/aselab/scala-activerecord
Latest version: 0.2.1
License: MIT

5. Features Version 0.1
Squeryl wrapper
Type-safe (most part)
Rails ActiveRecord-like operability
CoC (Convention over Configuration)
DRY (Don't Repeat Yourself) principles.
Auto transaction control
“Type-safed ActiveRecord model for Scala”

6. Features Version 0.2
Validations
Associations
Testing support
Improving query performance
Scala 2.10 support

7. 背景
Background

8. Why created? (1)
Scalaの大半のDBライブラリはSQLをWrapしたもの
関数型言語としての方向性としては正しい、かつ合理
的な方法
val selectCountries = SQL("Select * from Country")
val countries = selectCountries().map(row =>
row[String]("code") -> row[String]("name")
).toList
しかし、オブジェクト (Model) にマッピングするため
には全て自前で定義しないといけない
Not DRY!!

9. Why created? (2)
関連マッピングをまともに扱いたい・なるべく簡単に
使いたい
ClassごとにFinder methodを定義しなければならない
などDRYに書けない
本質的な処理についてだけ記述したいのにできない。
操作を書きたいのであってSQLを書きたいわけでは
ない
Not DRY!!!

10. Other libraries
Anorm
Slick (ScalaQuery)
Squeryl

11. (1) Anorm
ORMではなく、Model層を提供しない設計思想のため、
どうしてもClassごとに同じようなメソッドを定義せざ
るを得なくなる
case class Person(id: Pk[Long], name: String)
object Person {
def create(person: Person): Unit = {
DB.withConnection { implicit connection =>
SQL("insert into person(name) values ({name})").on(
'name -> person.name).executeUpdate()
}
}
...
}
Not DRY...

12. (2) Slick (ScalaQuery)
Queryの使用感は良いが、テーブル定義がやや冗長。
Modelとマッピングする場合、その対応をテーブルごと
に明示的に記述する必要がある
case class Member(id: Int, name: String, email: Option[String])
object Members extends Table[Member]("MEMBERS") {
def id = column[Int]("ID", O.PrimaryKey, O.AutoInc)
def name = column[String]("NAME")
def email = column[Option[String]]("EMAIL")
def * = id.? ~ name ~ email <> (Member, Member.unapply _)
}
Query interface is Good.
But, not DRY defining tables.

13. (3) Squeryl
ScalaのORMとしては最も良い出来
Queryに対してさらに条件を指定したQueryを作成すると
Sub-QueryなSQLが呼び出される
val query = from(table)(t => where(t.id.~ > 20) select(t))
from(query)(t => where(t.name like “%test%”) select(t))
Select * From
(Select * From table Where table.id > 20) q1
Where q1.name like “test”
Very nice ORM library.
Need to be aware of the SQL performance.

14. Improvements from Squeryl
Queryの合成結果が単なるSub Queryにならないように
Queryの条件をパフォーマンス劣化せず流用可能
val query = Table.where(_.id.~ > 20)
query.where(_.name like “%test%”).toList
Select * From table
Where
table.id > 20 and table.name like “test”
Generates more simple SQL statement.

15. Improvements from Squeryl
Iterable#iterator にアクセスした時点で inTransaction す
るよう変更
save, delete 時にデフォルトで inTransaction するように
もちろん明示的に transaction もできる
// auto inTransaction
query.toList
model.save
model.delete

16. Improvements from Squeryl
関連設定ルールをCoCで結び付けられるように
関連参照時のQueryがSubQueryにならないように
Eager loadingを実装
Simpler association definition rule.

17. Association definition (Squeryl)
object Schema extends Schema {
val foo = table[Foo]
val bar = table[Bar]
val fooToBar = oneToManyRelation(Foo, Bar).via(
(f, b) => f.barId === b.id
)
}
class Foo(var barId: Long) extends SomeEntity {
lazy val bar: ManyToOne[Bar] =
schema.fooToBar.right(this)
}
class Bar(var bar: String) extends SomeEntity {
lazy val foos: OneToMany[Foo] =
schema.fooToBar.left(this)
}

18. Association definition
(Scala ActiveRecord)
object Tables extends ActiveRecordTables {
val foo = table[Foo]
val bar = table[Bar]
}
class Foo(var barId: Long) extends ActiveRecord {
lazy val bar = belongsTo[Bar]
}
class Bar(var bar: String) extends ActiveRecord {
lazy val foos = hasMany[Foo]
}

19. Minimal example

20. Model implementation
case class Person(var name: String, var age: Int)
extends ActiveRecord
object Person
extends ActiveRecordCompanion[Person]
Schema definition
object Tables extends ActiveRecordTables {
val people = table[Person]
}

21. Create
val person = Person("person1", 25)
person.save
true
val person = Person("person1", 25).create
Person(“person1”, 25)

22. Read
Person.find(1)
Some(Person(“person1”))
Person.toList
List(Person(“person1”), ...)
Person.findBy(“name”, “john”)
Some(Person(“john”))
* Type-safe approach
Person.where(_.name === “john”).headOption
Some(Person(“john”))

23. Update
Person.find(1).foreach { p =>
p.name = “aaa”
p.age = 19
Callback hook
p.save Validations
}
Person.forceUpdate(_.id === 1)(
_.name := “aa”, _.age := 19
)

24. Delete
Person.where(_.name === “john”)
.foreach(_.delete)
Person.find(1) match {
case Some(person) => person.delete
case _ =>
}
Person.delete(1)

25. Query interface

26. Single object finder
val client = Client.find(10)
Some(Client) or None
val john = Client.findBy("name", "john")
Some(Client("john")) or None
val john25 = Client.findBy(("name", "john"), ("age", 25))
Some(Client("john", 25)) or None

27. Multiple object finder
Clients.where(c =>
c.name === "john" and c.age.~ > 25
).toList
Clients.where(_.name === "john")
.where(_.age.~ > 25)
.toList
Select
clients.name, clients.age, clients.id
From
clients
Where
clients.name = “john” and clients.age > 25

28. Using `Iterable` methods
val client = Client.head
First Client or RecordNotFoundException
val client = Client.lastOption
Some(Last Client) or None
val (adults, children) = Client.partition(_.age >= 20)
Parts of clients

29. Ordering
* Simple order (ORDER BY client.name)
Client.orderBy(_.name)
* Set order (use for 'asc' or 'desc')
Client.orderBy(_.name asc)
* Ordering by multiple fields
Client.orderBy(_.name asc, _.age desc)

30. Limit and Offset
Client.limit(10)
Client.page(2, 5)
Existence of objects
Client.exists(_.name like "john%")
true or false

31. Selecting specific fields
Client.select(_.name).toList
List[String]
Client.select(c => (c.name, c.age)).toList
List[(String, Int)]

32. Combining Queries
Clients.where(_.name like "john%”)
.orderBy(_.age desc)
.where(_.age.~ < 25)
.page(2, 5)
.toList
Select
clients.name, clients.age, clients.id
From
clients
Where
((clients.name like “john%”) and (clients.age < 25))
Order By
clients.age Desc
limit 5 offset 2

33. Cache control
QueryからIterableに暗黙変換される際に取得したListを
キャッシュとして保持
val orders = Order.where(_.age.~ > 20)
// execute SQL query, and cached query
orders.toList
// non-execute SQL query.
orders.toList

34. Validations

35. Annotation-based Validation
case class User(
@Required name: String,
@Length(max=20) profile: String,
@Range(min=0, max=150) age: Int
) extends ActiveRecord
object User extends
ActiveRecordCompanion[User]

36. Validation Sample
// it’s not save in the database
// because the object is not valid
val user = User("", “Profile”, 25).create
user.isValid
false
user.hasErrors
true
user.errors.messges
Seq("Name is required")
user.hasError("name")
true

37. More functional error handling...
User("John", “profile”, 20).saveEither match {
case Right(user) => println(user.name)
case Left(errors) => println(errors.messages)
}
"John"
User("", “profile”, 15).saveEither match {
case Right(user) => println(user.name)
case Left(errors) => println(errors.messages)
}
"Name is required"

38. Callbacks

39. Available hooks
•beforeValidation()
•beforeCreate()
•afterCreate()
•beforeUpdate()
•afterUpdate()
•beforeSave()
•afterSave()
•beforeDelete()
•afterDelete()

40. Callback example
case class User(login: String) extends ActiveRecord {
@Transient
@Length(min=8, max=20)
var password: String = _
var hashedPassword: String = _
override def beforeSave() {
hashedPassword = SomeLibrary.encrypt(password)
}
}
val user = User(“john”)
user.password = “raw_password”
user.save
Storing encrypted password

41. Associations

42. One-to-Many
case class User(name: String) extends ActiveRecord {
val groupId: Option[Long] = None
lazy val group = belongsTo[Group]
}
case class Group(name: String) extends ActiveRecord {
lazy val users = hasMany[User]
}

43. One-to-Many
val user1 = User("user1").create
val user2 = User("user2").create
val group1 = Group("group1").create
group1.users << user1
group1.users.toList
List(User("user1"))
user1.group.getOrElse(Group(“group2”))
Group("group1")

44. Association is Queryable
group1.users.where(_.name like “user%”)
.orderBy(_.id desc)
.limit(5)
.toList
Select
users.name, users.id
From
users
Where
((users.group_id = 1) AND (users.name like “user%”))
Order By
users.id Desc
limit 5 offset 0

45. Many-to-Many (HABTM)
case class User(name: String) extends ActiveRecord {
lazy val groups = hasAndBelongsToMany[Group]
}
case class Group(name: String) extends ActiveRecord {
lazy val users = hasAndBelongsToMany[User]
}

46. Many-to-Many (HABTM)
val user1 = User("user1").create
val user2 = User("user2").create
val group1 = Group("group1").create
val group2 = Group("group2").create
user1.groups := List(group1, group2)
user1.groups.toList
List(Group(“group1”), Group(“group2”))
group1.users.toList
List(User(“user1”))

47. Many-to-Many (hasManyThrough)
* Intermediate table's model
case class Membership(
userId: Long,
projectId: Long,
isAdmin: Boolean = false
) extends ActiveRecord
{
lazy val user = belongsTo[User]
lazy val group = belongsTo[Group]
}

48. Many-to-Many (hasManyThrough)
case class User(name: String) extends ActiveRecord {
lazy val memberships = hasMany[Membership]
lazy val groups =
hasManyThrough[Group, Membership](memberships)
}
case class Group(name: String) extends ActiveRecord {
lazy val memberships = hasMany[Membership]
lazy val users =
hasManyThrough[User, Membership](memberships)
}

49. Conditions option
case class Group(name: String) extends ActiveRecord {
lazy val adminUsers =
hasMany[User](conditions = Map("isAdmin" -> true))
}
group.adminUsers << user
user.isAdmin == true
ForeignKey option
case class Comment(name: String) extends ActiveRecord {
val authorId: Long
lazy val author =
belongsTo[User](foreignKey = “authorId”)
}

50. Joining tables
Client.joins[Order](
(client, order) => client.id === order.clientId
).where(
(client, order) => client.age.~ < 20 and order.price.~ > 1000
).select(
(client, order) => (client.name, client.age, order.price)
).toList
Select
clients.name, clients.age, orders.price
From
clients inner join orders on (clients.id = orders.client_id)
Where
((clients.age < 20) and (groups.price > 1000))

51. Eager loading associations
Solution to N + 1 queries problem
Order.includes(_.client).limit(10).map {
order => order.client.name
}.mkString(“n”)
Select orders.price, orders.id From orders limit 10 offset 0;
Select
clients.name, clients.age, clients.id
From
clients inner join orders on (clients.id = orders.client_id)
Where
(orders.id in (1,2,3,4,5,6,7,8,9,10))

52. Future

53. Future prospects
Compile time validation (using macro)
Serialization support
Web framework support
(Offers view helpers for Play 2.x and Scalatra)
STI, Polymorphic Association

54. Compile time validation
(using macro)
型安全性が確保できていない部分について
Scala macro を利用した型安全化
ActiveRecord#findBy(key: String, value: Any)
Association( fe
conditions: Map[String, Any], e- sa
foreignKey: String ttyp
) No
Type-safe binding configuration

55. Serialization support
パーサを個別に定義することなく、モデルを
定義するだけで済むように
JSON
Bind
Form Model XML
View
helper
Validation MessagePack
View

56. Web framework support
CRUD controller
Form helper
scala-activerecord-play2
scala-activerecord-scalatra
Code generator Controller, Model, View
sbt generate scaffold Person name:string:required age:int
scala-activerecord-play2-sbt-plugin
scala-activerecord-scalatra-sbt-plugin etc..

57. Thank you