Struggling with generic(s) repository methods - scala

Question

I have a Language model, table and repository. So far this works:
package repositories
import javax.inject.Inject
import Helper
import model.{Language, LanguageModel}
import play.api.Logger
import play.api.cache.SyncCacheApi
import slick.jdbc.JdbcProfile
import scala.concurrent.{ExecutionContext, Future}
import scala.util.{Failure, Success}
class LanguageRepository #Inject()(cache: SyncCacheApi, jdbcProfile: JdbcProfile, implicit val executionContext: ExecutionContext)
{
private val model = new LanguageModel(jdbcProfile)
import jdbcProfile.api._
def all(userName: String): Future[Seq[Language]] =
{
cache.get[Future[Seq[Language]]](buildCacheKey(userName)) match
{
case Some(x) => {Logger.info("[LanguageRepository](all) Found something in cache"); x}
case None => {
Logger.info("[LanguageRepository](all) Nothing useful to be found in cache, calling database now")
val result = retrieve(userName)
result.onComplete{
case Success(value) => if(!value.isEmpty) cache.set(buildCacheKey(userName), result)
case Failure(e) => ()
}
result
}
}
}
private def retrieve(userName: String): Future[Seq[Language]] =
{
// TODO extract this to a repositoryTrait and implement fallbacks etc
val db = Database.forURL(Helper.getDbUrl(), driver = Helper.getDbDriver())
db.run(model.all.result)
}
private def buildCacheKey(userName: String): String = s"$userName.languages"
}
Now I am struggling with the today past me left current me.
So I created this trait and wanted to let it be extended by LanguageRepository to get rid of that generic retrieve method that should be the same for all repositories/models. But sadly no luck so far:
trait Repository
{
type Entity
val model: Base
val profile: JdbcProfile
import profile.api._
protected def retrieve(userName: String): Future[Seq[Entity]] =
{
val db = Database.forURL(Helper.getDbUrl(), driver = Helper.getDbDriver())
db.run(model.all.result)
}
}
This is base:
trait Base
{
val dbProfile: JdbcProfile
import dbProfile.api._
type Entity
type EntityTable <: Table[Entity]
lazy val all = TableQuery[EntityTable]
}
Here I get one error >> class type required but Base.this.EntityTable found
class LanguageModel(databaseProfile: JdbcProfile) extends Base
{
override val dbProfile: JdbcProfile = databaseProfile
import dbProfile.api._
...
override type EntityTable = LanguageTable
}
Repository itself is not compiling either, because the types don't match. There are multiple problems and I am not sure where to start to solve them.

Answer 1

Your base table definition won't work like that. You need class types, maybe you should generics instead. Also, instead of creating multiple abstractions, start with only one abstraction and evolve from there. Try something along these lines:
class Repository[A, B <: Table[A]](t: TableQuery[B]) {
val model = t
//protected def retrieve ..
}
class LanguageModel(databaseProfile: JdbcProfile) extends Repository[Language, LanguageTable](TableQuery[LanguageTable]) {
//...
}
Get everything to compile first, then start adding the abstraction one class at a time.