Solid and Sustainable Development in Scala

Solid and Sustainable
Development in Scala
Kazuhiro Sera @seratch
ScalikeJDBC / Skinny Framework
Founder & Lead Developer

Ask Me Later!
• 3 mags for questioners at the end of this
session! Don’t miss it!

Who Am I
• Kazuhiro Sera • @seratch on Twitter/GitHub • Scala enthusiast since 2010 • ScalikeJDBC, Skinny Framework, AWScala
founder & project lead • A web developer at M3, Inc (We’re a Gold
Sponsor)

ScalikeJDBC
• scalikejdbc.org • “Scala-like JDBC” • Provides Scala-ish APIs • Started as a better querulous / Anorm • “Just write SQL and get things done” • QueryDSL for smoothness & type-safety • Stable enough: lots of companies already
use it in production

Dependencies
// build.sbt or project/Build.scala!
!
scalaVersion := “2.11.2” // or “2.10.4”!
!
libraryDependencies ++= Seq(!
“org.scalikejdbc” %% “scalikejdbc” % “2.1.1”,!
“com.h2database” % “h2” % “1.4.181”,!
“ch.qos.logback” % “logback-classic” % “1.1.2”!
)

Basic Usage
import scalikejdbc._!
!
ConnectionPool.singleton(!
“jdbc:h2:mem:matsuri”, !
“user”, “secret”)!
SQL statement!
(PreparedStatement)
!
DB autoCommit { implicit session =>!
Side effect !
with DB connection
sql”create table attendee (name varchar(32))”.execute.apply()!
val name = “seratch”!
sql”insert into attendee (name) values ($name)”.update.apply()!
}!
!
val names: Seq[String] = DB readOnly { implicit s =>!
sql”select name from attendee”!
.map(_.string(“name”)).list.apply()!
}
execute/update!
(JDBC operation)
Extractor

QueryDSL
case class Attendee(name: String)!
object Attendee extends SQLSyntaxSupport[Attendee] {!
def apply(rs: WrappedResultSet, a: ResultName[Attendee]) = !
new Attendee(rs.get(a.name))
}!
!
implicit val session = AutoSession!
!
!
val a = Attendee.syntax(“a”)!
val seratch: Option[Attendee] = withSQL {!
QueryDSL!
(Mostly SQL)
Actual SQL Query
select.from(Attendee as a).where.eq(a.name, “seratch”)!
}.map(rs => new Attendee(rs, a)).single.apply()!
!
// select a.name as n_on_a from attendee a where a.name = ?

Skinny Framework
• skinny-framework.org • “Scala on Rails” • For Rails / Play1 lovers • 1.0.0 is out on 28th March • Already several experiences in production • Full-stack features: Web infrastructure,
Scaffold generator, ORM, DB migration,
JSON stuff, HTTP client, Mail sender, Job
workers, Assets controller, etc..

Boot in 2 minutes
!
// install skinny command!
brew tap skinny-framework/alt!
brew install skinny!
!
// create app and start!
skinny new my app!
cd myapp!
skinny run!
!
// access localhost:8080 from your browser!

Model (DAO)
import skinny.orm._!
Entity
!
case class User(id: Long, name: Option[String])!
!
// companion: data mapper!
object User extends SkinnyCRUDMapper[User] {!
def defaultAlias = createAlias(“u”)!
def extract(rs: WrappedResultSet, u: ResultName[User])!
= autoConstruct(rs, u)
}!
CRUD Mapper Object!
!
(No need to be companion)
User.findById(123)!
User.count()!
User.createWithAttributes(‘name -> “Alice”)!
User.updateById(123).withAttributes(‘name -> “Bob”)!
User.deleteBy(sqls.eq(u.name, “Bob”))
Smooth APIs

Controller + Route
package controller!
class UsersController extends ApplicationController {!
def showUsers = {!
set(“users”, User.findAll())!
render(“/users/index”)
}
}!
!
// Routings!
object Controllers {!
Set value in request scope!
(Visible in views)
Expects “src/main/webapp/!
WEB-INF/views/users/index.html.ssp”
val users = new UsersController with Routes {!
get(“/users/”)(showUsers).as(‘showUsers)
}!
def mount(ctx: ServletContext): Unit = {!
users.mount(ctx)!
}
}

View Template
// src/main/webapp/WEB-INF/views/users/index.html.ssp!
!
<%@val users: Seq[User] %>!
!
<table class=“table”>!
#for (user <- users)!
<tr>!
<td>${user.id}</td>!
<td>${user.name}</td>!
</tr>!
#end!
</table>
import from request scope
Loop, if/else syntax!
in Scalate

Web Development
• Interactive feedback loop is most
important especially when changing UI • Actually Scala compilation is so slow that
waiting view templates compilation makes
developers much stressed • Skinny doesn’t compile all the view
templates when developing (unlike Twirl)

My Good Parts
for Solid and Safe
Development

My Good Parts
•Simplified Class-based OOP And
Immutable Data Structure
•Working On Problems Without
Overkill Abstraction
•Writing Tests Without Question
•Keep Infrastructure Lightweight
•No Surprises For Newcomer

Simplified Class-based
OOP
And Immutable
Data Structure

Class-based OOP
• Already so popular (Java, Ruby, Python ..) • Old style is friendly with mutability (e.g.
setters, bang methods), but that’s not a
prerequisite • OOP can be more solid and safer by
keeping immutability and avoiding
inheritance anti-patterns

Scala or Java 8?
• Scala case class is simpler than Java
beans with (great) Lombok • Scala high-order functions are simpler
than Java 8 Stream API • Immutability is well-treated in Scala • Fairness: Java decisively beats Scala in
comparison with compilation speed..

Immutability
• Do away with mutable states • Re-assignment? No way! Don’t use `var` • Immutability makes your apps not only
scalable but also more solid • When you modify a case class, call
#copy() and return new state instead of
using setters for mutability inside

Immutable Entity
// entity with behaviors!
case class User(id: Long, name: Option[String])!
extends SkinnyRecord[User] {!
override def skinnyCRUDMapper = User
}!
// data mapper!
object User extends SkinnyCRUDMapper[User] {!
override def defaultAlias = createAlias(“u”)!
override def extract(rs: WrappedResultSet, u: ResultName[User])!
= autoConstruct(rs, u)
}!
!
val noNames: Seq[User] = User.where(‘name -> “”).apply()!
val anons: Seq[User] = noNames.map { user => !
user.copy(name = “Anonymous”).save()!
}
Both of “noNames” and
“anions” are immutable

Trait Chaos
• Mixing traits can show you terrible chaos • We should have self-discipline • Prefer `override` modifier to detect API
changes when mixing many traits • Collect the same sort of traits and place
them in same place to avoid code
duplication or unwanted complexity

Web Controller
package controller!
class MainController extends ApplicationController !
with concern.TimeLogging {!
def index = logElapsedTime { render(“/main/index”) }!
}!
!
// for controllers!
package controller.concern!
trait TimeLogging { self: SkinnyController with Logging =>!
The “concern” just follows Rails style.
Anyway, naming should be simple and!
easy-to-understand for anyone
def millis: Long = System.currentTimeMillis !
def logElapsedTime[A](action: => A): A = {!
val before = millis!
val result = action!
logger.debug(“Elapsed time: ${millis - before} millis”)!
result
}!
}

Coding Style Tips
• Use sbt-scalariform without question
(similar: go-lang’s fmt) • Don’t toss similar classes or traits into
single scala file except `sealed` pattern • Don’t place classes under different
package directory (although it’s possible) • Do you really need cake pattern? • Prefer eloquent method signature than
explaining a lot in scaladocs

Working On
Problems Without
Overkill Abstraction

The Real As-Is
• Abstraction often improves things, but
that’s not always the best way to solve
real-world problems • I/O issue is a typical case that we should
comprehend problems as-is • Database access / SQL is not a collection
but just an external I/O operation • Overkill abstraction makes your code
difficult to maintain for other developers

Don’t Hide the SQL
• “You don’t need another DSL to access
relational databases” - Anorm • You must recognize what is working
effectively in the SQL layer • Utility to write DAO easily is fine but
hiding SQL is not good • Need to grab the cause from raw queries
when dealing with troubles (comfortable
logging also can help)

SQL Ops As-Is
// A programmer belongs to a company and has several skills!
!
implicit val session = AutoSession!
!
val p: Option[Programmer] = withSQL {!
I believe everybody can
understand this code
select.from(Programmer as p)!
.leftJoin(Company as c).on(p.companyId, c.id)!
.leftJoin(ProgrammerSkill as ps).on(ps.programmerId, p.id)!
.leftJoin(Skill as s).on(ps.skillId, s.id)!
.where.eq(p.id, 123).and.isNull(p.deletedAt)!
}!
.one(rs => Programmer(rs, p, c))!
Extracts one-to-many
.toMany(rs => Skill.opt(rs, s))!
relationships here
.map { (programmer, skills) => programmer.copy(skills = skills) }!
.single!
.apply()

Skinny ORM
• ORM built on ScalikeJDBC • Highly inspired by Rails ActiveRecord • SQL queries for CRUD apps are common
enough, so it’s reasonable to avoid writing
mostly same code everywhere • Skinny ORM doesn't prevent you from
using ScaikeJDBC APIs directly • A part of Skinny Framework but you can
use it in Play apps too

Dependencies
// build.sbt or project/Build.scala!
!
scalaVersion := “2.11.2” // or “2.10.4”!
!
libraryDependencies ++= Seq(!
//“org.scalikejdbc” %% “scalikejdbc” % “2.1.1”,!
“org.skinny-framework” %% “skinny-orm” % “1.3.1”,!
“com.h2database” % “h2” % “1.4.181”,!
“ch.qos.logback” % “logback-classic” % “1.1.2”!
)

Mappers
// entities!
case class Company(id: Long, name: String)!
case class Employee(id: Long, name: String,!
companyId: Long, company: Option[Company])!
!
// mappers!
object Company extends SkinnyCRUDMapper[Company] {!
def extract(rs: WrappedResultSet, rn: ResultName[Company]) =!
autoConstruct(rs, rn)
}!
object Employee extends SkinnyCRUDMapper[Employee] {!
def extract(rs: WrappedResultSet, rn: ResultName[Employee]) =!
autoConstruct(rs, rn, “company”)!
// simple association definition!
lazy val companyRef = belongsTo[Company](!
Company, (e, c) => e.copy(company = c))
}

Reasonable?
Right, these CRUD operations are not SQL-ish. However, I believe
they’re reasonable because these patterns are already common enough.
!
!
val companyId = Company.createWithAttributes(‘name -> “Sun”)!
val empId = Employee.createWithAttributes(!
‘name -> “Alice”, ‘companyId -> companyId)!
!
val emp: Option[Employee] = Employee.findById(empId)!
val empWithCompany: Option[Employee] = !
Employee.joins(companyRef).findById(123)!
!
Company.updateById(companyId).withAttributes(‘name -> “Oracle”)!
!
val e = Employee.defaultAlias!
Employee.deleteBy(sqls.eq(e.id, empId))!
Using ScalikeJBDC API!
Company.deleteById(companyId)
is also possible

Writing Tests
Without
Question

Not Only Compiler
• It’s true that compiler helps you by
detecting mistakes in coding • Writing tests is a reasonable way to verify
your code meets requirements /
specifications as expected • You can’t skip automated tests even if
your apps are written in Scala

scoverage
• At this time, the only option available for
us is scoverage (SCCT inheritor) • Add the dependency into your projects
right now if you don’t use it yet

Keep
Infrastructure
Lightweight

Avoid SBT Hacks
• sbt is not so easy for Scala newbies,
upgrading sbt is all the more so • Play depends on sbt version (e.g. Play 2.1
w/ sbt 0.12), upgrading Play is about not
Play API but sbt things • Your own sbt plugins/hacks makes your
projects difficult to maintain for a long
period and involve others • Don’t try to do everything there

Skinny TaskRunner
• Just want a simple and “rake”-like task
runner (no sbt plugin) • Simplistic but pragmatic idea: “mainClass”
of “task” sbt project can be dispatcher of
task runner system • Tasks are written in Scala (no sbt plugin) • Not only writing code but upgrading
scala/sbt version become pretty easy

Tasks
// sbt settings!
// mainClass := Some("TaskRunner")!
!
// task/src/main/scala/TaskRunner.scala!
object TaskRunner extends skinny.task.TaskLauncher {!
register("assets:precompile", (params) => {!
val buildDir = params.headOption.getOrElse(“build")!
// AssetsPrecompileTask is a Scala object!
skinny.task.AssetsPrecompileTask.main(Array(buildDir))!
})!
}!
Pure Scala function!
!
// skinny task:run assets:precompile [dir]
task name
mainClass as the dispatcher

Use Only Essentials
• The same issue as Ruby gems, what’s
worse, Scala’s eco-system is still so
smaller than Ruby’s one • Binary incompatibility makes existing
libraries outdated every Scala major
version release • Are you really ready to fork them? • Using Java assets (e.g. commons)
internally is also worth thinking about

Can Feel Welcome?
• Is joining your Scala projects easy? Can
newcomer understand overview at once? • Don’t stick to doing on the sbt, don’t
disfavor using other tools (e.g. Grunt) • Well-known style (e.g. Rails style) is
preferred for collaborative works • Is asynchronosity really required now? • Indeed, your DSL is very simple but easy
to modify them (for others)?

Newcomers may not
know Scala well.
Attract them to Scala!
(Don’t scare them)

AMA! #ScalaMatsuri2
• Unconference tomorrow • “Ask Me Anything” • ScalikeJDBC • Skinny Framework • AWScala • Anything else!

Thanks
• Amazing “Maturi Urakata” (the
conference volunteer staff) • Great invited speakers • You all here!

Solid and Sustainable Development in Scala

Recommended

More Related Content

What's hot (17)

Viewers also liked (6)

Similar to Solid and Sustainable Development in Scala (20)

More from scalaconfjp (20)

Recently uploaded (20)

Solid and Sustainable Development in Scala