using package in Scala? - scala

Question

I have a scala project that uses akka. I want the execution context to be available throughout the project. So I've created a package object like this:
import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import com.datastax.driver.core.Cluster
package object connector {
implicit val system = ActorSystem()
implicit val mat = ActorMaterializer()
implicit val executionContext = executionContext
implicit val session = Cluster
.builder
.addContactPoints("localhost")
.withPort(9042)
.build()
.connect()
}
In the same package I have this file:
import akka.stream.alpakka.cassandra.scaladsl.CassandraSource
import akka.stream.scaladsl.Sink
import com.datastax.driver.core.{Row, Session, SimpleStatement}
import scala.collection.immutable
import scala.concurrent.Future
object CassandraService {
def selectFromCassandra()() = {
val statement = new SimpleStatement(s"SELECT * FROM animals.alpakka").setFetchSize(20)
val rows: Future[immutable.Seq[Row]] = CassandraSource(statement).runWith(Sink.seq)
rows.map{item =>
print(item)
}
}
}
However I am getting the compiler error that no execution context or session can be found. My understanding of the package keyword was that everything in that object will be available throughout the package. But that does not seem work. Grateful if this could be explained to me!

Answer 1

Your implementation must be something like this, and hope it helps.
package.scala
package com.app.akka
package object connector {
// Do some codes here..
}
CassandraService.scala
package com.app.akka
import com.app.akka.connector._
object CassandraService {
def selectFromCassandra() = {
// Do some codes here..
}
}

Answer 2

You have two issue with your current code.
When you compile your package object connector it is throwing below error
Error:(14, 35) recursive value executionContext needs type
implicit val executionContext = executionContext
Issue is with implicit val executionContext = executionContext line
Solution for this issue would be as below.
implicit val executionContext = ExecutionContext
When we compile CassandraService then it is throwing error as below
Error:(17, 13) Cannot find an implicit ExecutionContext. You might pass
an (implicit ec: ExecutionContext) parameter to your method
or import scala.concurrent.ExecutionContext.Implicits.global.
rows.map{item =>
Error clearly say that either we need to pass ExecutionContext as implicit parameter or import scala.concurrent.ExecutionContext.Implicits.global. In my system both issues are resolved and its compiled successfully. I have attached code for your reference.
package com.apache.scala
import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import com.datastax.driver.core.Cluster
import scala.concurrent.ExecutionContext
package object connector {
implicit val system = ActorSystem()
implicit val mat = ActorMaterializer()
implicit val executionContext = ExecutionContext
implicit val session = Cluster
.builder
.addContactPoints("localhost")
.withPort(9042)
.build()
.connect()
}
package com.apache.scala.connector
import akka.stream.alpakka.cassandra.scaladsl.CassandraSource
import akka.stream.scaladsl.Sink
import com.datastax.driver.core.{Row, SimpleStatement}
import scala.collection.immutable
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future
object CassandraService {
def selectFromCassandra() = {
val statement = new SimpleStatement(s"SELECT * FROM animals.alpakka").setFetchSize(20)
val rows: Future[immutable.Seq[Row]] = CassandraSource(statement).runWith(Sink.seq)
rows.map{item =>
print(item)
}
}
}