I want to set up doobie inside the AsyncFunction of apache Flink but it needs an implicit read instance of output. on the other hand, I can not send Read[Out] as an implicit parameter because the AsyncFunction needs to be serializable and this implicit value violates this rule:
package FlinkHelpers
import Configs.JdbConfig
import doobie.hikari._
import doobie._
import doobie.implicits._
import doobie.util.ExecutionContexts
import cats._
import cats.data._
import cats.effect.IO.asyncForIO
import cats.effect._
import cats.implicits._
import fs2.Stream
import cats.effect.unsafe.implicits.global
import org.apache.flink.runtime.concurrent.Executors
import org.apache.flink.streaming.api.scala.async.{AsyncFunction, ResultFuture}
import scala.concurrent.{ExecutionContext, Future}
import scala.util.Try
class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(implicit r:Read[Out]) extends AsyncFunction[In,(In, Out)] {
lazy val transactor: Resource[IO, HikariTransactor[IO]] = {
for {
ce <- ExecutionContexts.fixedThreadPool[IO](32)
xa <- HikariTransactor.newHikariTransactor[IO](
"org.postgresql.Driver",
"jdbc:postgresql://localhost:5433/doobie",
"psql",
"110271",
ce
)
} yield xa
}
/** The context used for the future callbacks */
implicit lazy val executor: ExecutionContext = ExecutionContext.fromExecutor(Executors.directExecutor())
override def asyncInvoke(input: In, resultFuture: ResultFuture[(In, Out)]): Unit = {
val v2: IO[Out] = transactor.use[Out] { xa2: HikariTransactor[IO] => {
sql"select code,name,population,gnp from Out limit 1"
.query[Out] // Query0[String]
.unique // ConnectionIO[List[String]]
.transact(xa2) // IO[List[String]]
}
}
val future = v2.unsafeToFuture()
future.onSuccess({
case result: Out => resultFuture.complete(List((input, result)))
})
}
}
on the other hand scala does not allow me to make the r
field transiend
does anyone have any idea how I can solve this?
r
in class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(r:Read[Out])...
is a constructor parameter but Scala can generate private[this]
field for it too:
Disambiguate constructor parameter with same name as class field of superclass (answer)
Try to add annotation @transient
class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(@transient private[this] implicit val r:Read[Out])...
or
class AsyncDatabaseRequestOne[In,Out](configs:JdbConfig)(@(transient @field) private[this] implicit val r:Read[Out])...
Since @transient
is defined already with @field
@field
final class transient extends scala.annotation.StaticAnnotation
I guess in our case @field
meta-annotation is not necessary.