Multiple slick `column`s for the same DB column break projection - scala

Question

I'm new to Slick thus I'm not sure whether the problem caused by incorrect usage of implicits or Slick doesn't allow doing what I'm trying to do.
In short I use Slick-pg extension for JSONB support in Postgres. I also use spray-json to deserialize JSONB fields into case classes.
In order to automagically convert columns into objects I wrote generic implicit JsonColumnType that you can see below. It allows me to have any case class for which I defined json formatter to be converted to jsonb field.
On the other hand I want to have alias of JsValue type for the same column so that I can use JSONB-operators.
import com.github.tminglei.slickpg._
import com.github.tminglei.slickpg.json.PgJsonExtensions
import org.bson.types.ObjectId
import slick.ast.BaseTypedType
import slick.jdbc.JdbcType
import spray.json.{JsValue, RootJsonWriter, RootJsonReader}
import scala.reflect.ClassTag
trait MyPostgresDriver extends ExPostgresDriver with PgArraySupport with PgDate2Support with PgRangeSupport with PgHStoreSupport with PgSprayJsonSupport with PgJsonExtensions with PgSearchSupport with PgNetSupport with PgLTreeSupport {
override def pgjson = "jsonb" // jsonb support is in postgres 9.4.0 onward; for 9.3.x use "json"
override val api = MyAPI
private val plainAPI = new API with SprayJsonPlainImplicits
object MyAPI extends API with DateTimeImplicits with JsonImplicits with NetImplicits with LTreeImplicits with RangeImplicits with HStoreImplicits with SearchImplicits with SearchAssistants { //with ArrayImplicits
implicit val ObjectIdColumnType = MappedColumnType.base[ObjectId, Array[Byte]](
{ obj => obj.toByteArray }, { arr => new ObjectId(arr) }
)
implicit def JsonColumnType[T: ClassTag](implicit reader: RootJsonReader[T], writer: RootJsonWriter[T]) = {
val columnType: JdbcType[T] with BaseTypedType[T] = MappedColumnType.base[T, JsValue]({ obj => writer.write(obj) }, { json => reader.read(json) })
columnType
}
}
}
object MyPostgresDriver extends MyPostgresDriver
Here is how my table is defined (minimized version)
case class Article(id : ObjectId, ids : Ids)
case class Ids(doi: Option[String], pmid: Option[Long])
class ArticleRow(tag: Tag) extends Table[Article](tag, "articles") {
def id = column[ObjectId]("id", O.PrimaryKey)
def idsJson = column[JsValue]("ext_ids")
def ids = column[Ids]("ext_ids")
private val fromTuple: ((ObjectId, Ids)) => Article = {
case (id, ids) => Article(id, ids)
}
private val toTuple = (v: Article) => Option((v.id, v.ids))
def * = ProvenShape.proveShapeOf((id, ids) <> (fromTuple, toTuple))(MappedProjection.mappedProjectionShape)
}
private val articles = TableQuery[ArticleRow]
Finally I have function that looks up articles by value of json field
def getArticleByDoi(doi : String): Future[Article] = {
val query = (for (a <- articles if (a.idsJson +>> "doi").asColumnOf[String] === doi) yield a).take(1).result
slickDb.run(query).map { items =>
items.headOption.getOrElse(throw new RuntimeException(s"Article with doi $doi is not found"))
}
}
Sadly I get following exception in runtime
java.lang.ClassCastException: spray.json.JsObject cannot be cast to server.models.db.Ids
The problem is in SpecializedJdbcResultConverter.base where ti.getValue is being called with wrong ti. It should be slick.driver.JdbcTypesComponent$MappedJdbcType but instead it's com.github.tminglei.slickpg.utils.PgCommonJdbcTypes$GenericJdbcType. As result wrong type is passed into my tuple converter.
What makes Slick choose different type for column even though there is explicit definition of projection in table row class ?
Sample project that demonstrates the issue is here.