Conditionally map a nullable field to None value in Slick - scala

Question

In Slick 2.1, I need to perform a query/map operation where I convert a nullable field to None if it contains a certain non-null value. Not sure whether it matters or not, but in my case the column type in question is a mapped column type. Here is a code snippet which tries to illustrate what I'm trying to do. It won't compile, as the compiler doesn't like the None.
case class Record(field1: Int, field2: Int, field3: MyEnum)
sealed trait MyEnum
val MyValue: MyEnum = new MyEnum { }
// table is a TableQuery[Record]
table.map { r => (
r.field1,
r.field2,
Case If (r.field3 === MyValue) Then MyValue Else None // compile error on 'None'
)
}
The error is something like this:
type mismatch; found : None.type required: scala.slick.lifted.Column[MyEnum]
Actually, the reason I want to do this is that I want to perform a groupBy in which I count the number of records whose field3 contains a given value. I couldn't get the more complicated groupBy expression working, so I backed off to this simpler example which I still can't get working. If there's a more direct way to show me the groupBy expression, that would be fine too. Thanks!
Update
I tried the code suggested by #cvogt but this produces a compile error. Here is a SSCCE in case anyone can spot what I'm doing wrong here. Compile fails with "value ? is not a member of Int":
import scala.slick.jdbc.JdbcBackend.Database
import scala.slick.driver.H2Driver
object ExpMain extends App {
val dbName = "mydb"
val db = Database.forURL(s"jdbc:h2:mem:${dbName};DB_CLOSE_DELAY=-1", driver = "org.h2.Driver")
val driver = H2Driver
import driver.simple._
class Exp(tag: Tag) extends Table[(Int, Option[Int])](tag, "EXP") {
def id = column[Int]("ID", O.PrimaryKey)
def value = column[Option[Int]]("VALUE")
def * = (id, value)
}
val exp = TableQuery[Exp]
db withSession { implicit session =>
exp.ddl.create
exp += (1, (Some(1)))
exp += (2, None)
exp += (3, (Some(4)))
exp.map { record =>
Case If (record.value === 1) Then 1.? Else None // this will NOT compile
//Case If (record.value === 1) Then Some(1) Else None // this will NOT compile
//Case If (record.value === 1) Then 1 Else 0 // this will compile
}.foreach {
println
}
}
}

Answer 1

I need to perform a query/map operation where I convert a nullable field to None if it contains a certain non-null value
Given the example data you have in the update, and pretending that 1 is the "certain" value you care about, I believe this is the output you expect:
None, None, Some(4)
(for rows with IDs 1, 2 and 3)
If I've understood the problem correctly, is this what you need...?
val q: Query[Column[Option[Int]], Option[Int], Seq] = exp.map { record =>
Case If (record.value === 1) Then (None: Option[Int]) Else (record.value)
}
...which equates to:
select (case when ("VALUE" = 1) then null else "VALUE" end) from "EXP"

Answer 2

You need to wrap MyValue in an Option, so that both outcomes of the conditional are options. In Slick 2.1 you use the .? operator for that. In Slick 3.0 it will likely be Rep.Some(...).
Try
Case If (r.field3 === MyValue) Then MyValue.? Else None
or
Case If (r.field3 === MyValue) Then MyValue.? Else (None: Option[MyEnum])