Rafael Bagmanov «Scala in a wild enterprise»

Scala in a wild
enterprise
Rafael Bagmanov
( Grid Dynamics )
the?

In what use cases (types of applications)
does Scala make the least sense?

"Database front end, CRUD apps.
Most of the boring apps that are built with
Struts and Spring"
David Pollak
"Barriers to scala adoption" Infoq.com

OpenGenesis
github.com/griddynamics/OpenGenesis

● open source - open-genesis.org
● 2 years of development
● > 50 KLOC of scala code
● successfully deployed to production in one
large american financial institution
● Buzzwords: continuous deployment, cloud,
chef, devops, aws, openstack
OpenGenesis
Deployment orchestration tool

● Integration with legacy apps and data (lots of
SOAP and xml)
● sophisticated security policies
● IT department separated from development
team
● J2EE Containers everywhere
● Risk averse
Enterprise characteristics

Typical "lightweight" j2ee stack
Web layer
Service layer
Data access layer
DB
Spring MVC
Spring
JPA

j2ee stack. Scala edition
Web layer
Service layer
Data access layer
DB
Spring MVC + scala magic
Spring + scala implicits
JPA Squeryl

j2ee stack. Scala edition
Web layer
Service layer
Data access layer
DB
Spring MVC
Spring
Squeryl
WAR

j2ee stack. Scala edition + scala
goodness
Web layer
Service layer
Data access layer
DB
Spring MVC
Spring
Squeryl
Workflow distributed
engine
Akka
WAR

● DI fits almost nicely with scala
Spring with scala

class GenesisRestController {
@Autowired var genesisService: GenesisService = _
}
class GenesisRestController {
@BeanProperty var genesisService: GenesisService = _
}
class GenesisRestController (genesisService: GenesisService) {}
Spring with scala

○ "Everything is a trait" approach can't be done
Spring with scala

○ Be aware of type inference in @Configuration bean
trait Service
class ServiceImpl extends Service
@Configuration
class ServiceContext {
@Bean def service = new ServiceImpl
}
Spring with scala

○ Be aware of type inference in @Configuration bean
trait Service
class ServiceImpl extends Service
@Configuration
class ServiceContext {
@Bean def service: Service = new ServiceImpl
}
Spring with scala

● Rich spring templates libraries.
Spring with scala

springLdapTemplate.authenticate("user", "*", "password", new
AuthenticationErrorCallback {
def execute(e: Exception) {log.error(e)}
})
Spring with scala

springLdapTemplate.authenticate("user", "*", "password", new
AuthenticationErrorCallback {
def execute(e: Exception) {log.error(e)}
})
springLdapTemplate.authenticate("user", "*", "password", log.error(_))
Spring with scala

springLdapTemplate.authenticate("user", "*", "password", log.error(_))
implicit def authErrorCallbackWrapper(func:(Exception) => Any) = {
new AuthenticationErrorCallback {
def execute(exception: Exception): Unit = func(exception)
}
}
Spring with scala

● AOP for free (almost)
Spring with scala

○ Be aware of naming in debug info
def findUsers(projectId: Int) {
dao.findUsers(projectId)
}
def findUsers2(projectId: Int) {
dao.allUsers().filter(_.projectId == projectId)
}
Spring with scala

○ Be aware of naming in debug info
def findUsers(projectId: Int) { // debugIfo: name "projectId"
dao.findUsers(projectId)
}
def findUsers2(projectId: Int) { // debugInfo: name "projectId$"
dao.allUsers().filter(_.projectId == projectId)
}
Spring with scala

● Spring security just works
Spring with scala

● Lightweight ORM written in scala
Squeryl

Squeryl
class Workflow(override val id: Int) extends KeyedEntity[Int]

Squeryl
object GS extends Schema {
val workflows = table[Workflow]
}

Squeryl
object GS extends Schema {
val workflows = table[Workflow]
}
def find(workflowId: Int) = from(GS.workflows)(w =>
where(w.id === workflowId)
select (w)
orderBy(w.id desc)
)

○ First class support for scala collections, options, etc
Squeryl

○ Integrates with spring transaction management
(not out of the box)
Squeryl

○ Integrates with spring transaction management
(not out of the box)
Squeryl
@Transactional(propagation = REQUIRES_NEW)
def find(workflowId: Int) = from(GS.workflows)(w =>
where(w.id === workflowId)
select (w)
orderBy(w.id desc)
)

Squeryl
○ Likes heap in the same proportion as
Hibernate does
hibernate squeryl

○ Likes heap in the same proportion as
Hibernate does
○ Lot's of "black magic" in source code
Squeryl

● Internal scala DSL for writing queries
○ Type safe queries - compile time syntax check
Squeryl

Squeryl

○ Fallback on native sql is not easy
Squeryl

○ Lots of implicits drives IDE crazy and
increases compilation time
Squeryl

○ Lots of implicits drives IDE crazy and
increase compilation time
○ The approach is somewhat flawed (opinion)
Squeryl

Web layer: Spring MVC
lift-json
scala magic

● RESTfull web services
Web layer
case class User (
@NotBlank username: String,
@Email @Size(min = 1, max = 256) email: String,
password: Option[String]
)
@Controller
@RequestMapping(Array("/rest/users"))
class UsersController {
@RequestMapping(method = Array(RequestMethod.POST))
@ResponseBody
def create(@RequestBody @Valid request: User): User = userService.create(request)
}

● RESTfull web services
● Easy to make Hypermedia REST with
implicits
Web layer
@Controller
@RequestMapping(Array("/rest/users"))
class UsersController {
import com.griddynamics.genesis.rest.links.Hypermedia._
@RequestMapping(method = Array(RequestMethod.POST))
@ResponseBody
def create(@RequestBody @Valid request: User): Hypermedia[User] = {
userService.create(request).withLink("/rest/users", LinkType.SELF)
}

Ехал Акка через Акка
Смотрит Акка в Акка Акка
Сунул Акка Акка в Акка
Акка Акка Акка Акка *
* Ode to Akka in russian

● Hiring is hard
○ Scala is a talent attraction
Challenges

● Hiring is hard
○ Scala is a talent attraction
○ In avg: 0.5 interview per month
Challenges

● Hiring is hard
● Settling team standards and code
convention
Challenges

● Hiring is hard
convention
○ Tools are not there yet
Challenges

● Hiring is hard
convention
○ Between "OCaml" and "Java" fires
Challenges

● Hiring is hard
convention
○ Between "OCaml" and "Java" fires
○ "Effective scala" by Twitter and "Scala style guide"
might help (a bit)
Challenges

The greatest code-review mystery of
all times
if (option.isDefined) {
..
}
option.foreach { .. }
option match {
case Some(x) => ..
case None => ..
}
How to deal with scala.Option
?

1. Denial
2. Anger
3. Bargaining
4. Depression
5. Acceptance
5 stages of grief

Rafael Bagmanov «Scala in a wild enterprise»

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