The document discusses how to build a contacts service that stores contact information in a database and exposes it via JSON endpoints. It describes creating case classes to represent contacts and emails in Scala, implementing JSON serialization and deserialization using Play JSON, defining a database schema using Slick, and writing methods to save contacts to and load them from the database.

1. JSON OBJECTS RDBMSTO TO
Stephen Kemmerling
@42eng

2. CONTACTS AS A SERVICE
Should have JSON endpoints for
• Store contact information
• Retrieval by Name
Contacts as a Service
https://github.com/FortyTwoEng/
Contacts-As-A-Service/blob/master/
app/controllers/Application.scala

3. • OO Representation
• Handle JSON requests and convert to OO
• Save to DB/Load from DB
What do we need?

4. • OO Representation
• Handle JSON requests and convert to OO
• Save to DB/Load from DB
What do we need?

5. SCALA REPRESENTATION
case class Email(addr: String)
case class Contact(
name: String,
phone: Option[Int],
email: Option[Email]
)

6. • OO Representation
• Handle JSON requests and convert to OO
• Save to DB/Load from DB
What do we need?

7. SENDING JSON RESPONSES
def lookup(name: String) = Action { request =>
val contacts : Seq[Contact] = loadFromDb(name)
val contactsJson : Seq[JsValue] = contacts.map(Json.toJson(_))
Ok(JsArray(contactsJson))
}

8. TO/FROM JSON
trait Format[T] {
def reads(json: JsValue): JsResult[T]
def writes(obj: T): JsValue
}

9. MACROS!
object Contact {
implicit val format: Format[Contact] =
Json.format[Contact]
}
Almost, but not quite: Can’t deal with Email
case class Email(addr: String)
case class Contact(
name: String,
phone: Option[Int],
email: Option[Email]
)
MAGIC!

10. FORMAT BY HAND
object Email {
implicit format : Format[Email] = Json.format[Email]
}
Let’s not be lazy

11. FORMAT BY HAND
object Email {
implicit val format = new Format[Email]{
def reads(json: JsValue) : JsResult[Email] = {
json match{
case JsString(s) => JsSuccess(Email(s))
case _ => JsError()
}
}
def writes(email: Email) : JsValue = {
JsString(email.addr)
}
}
}

12. ACCEPTING JSON
REQUESTS
def store(name: String) = Action(parse.tolerantJson)
{ request =>
val phoneJson : JsValue = request.body "phone"
val phone : Option[Int] = phoneJson.asOpt[Int]
val email = (request.body "email").asOpt[Email]
val contact = Contact(name, phone, email)
saveToDb(contact)
Ok(“”)
}

13. ALL TOGETHER NOW
def lookup(name: String) = Action { request =>
val contacts : Seq[Contact] = loadFromDb(name)
val contactsJson : Seq[JsValue] =
contacts.map(Json.toJson(_))
Ok(JsArray(contactsJson))
}
def store(name: String) = Action(parse.tolerantJson)
{ request =>
val phoneJson : JsValue = request.body "phone"
val phone : Option[Int] = phoneJson.asOpt[Int]
val email = (request.body "email").asOpt[Email]
val contact = Contact(name, phone, email)
saveToDb(contact)
Ok(“”)
}

14. • OO Representation
• Handle JSON requests and convert to OO
• Save to DB/Load from DB
What do we need?

15. SLICK TABLE DEFINITION
object Contacts extends Table[Contact]("contacts") {
def name = column[String]("name", O.PrimaryKey)
def phone = column[Int]("phone", O.Nullable)
def email = column[Email]("email", O.Nullable)
def * = name ~ phone.? ~ email.?
<> (Contact.apply _, Contact.unapply _)
}

16. INSERTS AND LOOKUPS
def saveToDb(contact: Contact) =
database.withSession{ implicit session: Session =>
Contacts.*.insert(contact)
}
def loadFromDb(name: String) =
database.withSession{ implicit session: Session =>
(for (row <- Contacts if row.name===name) yield row).list
}

17. SLICK TABLE DEFINITION
object Contacts extends Table[Contact]("contacts") {
def name = column[String]("name", O.PrimaryKey)
def phone = column[Int]("phone", O.Nullable)
def email = column[Email]("email", O.Nullable)
def * = name ~ phone.? ~ email.?
<> (Contact.apply _, Contact.unapply _)
}
def saveToDb(contact: Contact) =
database.withSession{ implicit session: Session =>
Contacts.*.insert(contact)
}
def loadFromDb(name: String) =
database.withSession{ implicit session: Session =>
(for (row <- Contacts if row.name===name) yield row).list
}

18. TYPE MAPPER
implicit object typeMapper extends BaseTypeMapper[Email] {
def apply(profile: BasicProfile) : TypeMapperDelegate[Email] = {
val delegate = profile.typeMapperDelegates.stringTypeMapperDelegate
new TypeMapperDelegate[Email] {
def sqlType = delegate.sqlType
def setValue(value: Email, p: PositionedParameters) =
delegate.setValue(value.addr, p)
def setOption(valueOpt: Option[Email], p: PositionedParameters) =
delegate.setOption(valueOpt.map(_.addr), p)
def nextValue(r: PositionedResult): Email =
Email(delegate.nextValue(r))
def sqlTypeName = delegate.sqlTypeName
def updateValue(value: Email, r: PositionedResult) =
delegate.updateValue(value.addr, r)
def zero = Email("towel@42go.com")
}
}
}

19. e class Email(addr: String)
ect Email {mplicit val format = new
mat[Email]{def reads(json: JsValue) :
sult[Email] = {
json match{case JsString(s) =>
cess(Email(s))case _ => JsError()
}
f writes(email: Email) :
e = {sString(email.addr)
p(name: String) =
rse.json) { request =>
acts : Seq[Contact] =
(name)actsJson : Seq[J
ts.map(J
object Contacts extends
Table[Contact]("contacts") {
def name = column[String]
("name", O.PrimaryKey)
def phone = column[Int]
("phone", O.Nullable)
def email = column[Email]
("email", O.Nullable)
def * = name ~ phone.? ~
email.?
<> (Contact.apply _,
Contact.unapply _)
}
def saveToDb(contact:
database.with
session
meters) =
[Email], p:
gate.setOption(valueOpt.map(_.addr),
Value(r: PositionedResult): Email =
delegate.nextValue(r))
def sqlTypeName = delegate.sqlTypeName
def updateValue(value: Email, r: PositionedResult) =
delegate.updateValue(value.addr, r)
def zero = Email("towel@42go.com")
}
}
}
case class Contact(
name: String,
phone: Option[Int],
email: Option[Email]
)
object Contact {
implicit format : Format[Contact] =
}
SOURCE: https://github.com/FortyTwoEng/Contacts-As-A-Service
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