Slick 3.1.1 warning when using nullable foreign key
Today while I was working with Slick I stumbled onto a deprecation warning and had a short adventure through the documentation trying to figure out how to remove said warning and do what I was doing the right way.
The warning itself was like this:
[warn] /Path/To/Thing.scala:37: method columnToOptionColumn in trait API is deprecated: Use an explicit conversion to an Option column with `.?` [warn] lazy val defaultUnitIdFk = foreignKey("fk_my_exciting_fk_constraintname", defaultUnitId, UnitTable.Unit)(u => u.unitId, onUpdate = ForeignKeyAction.SetNull, onDelete = ForeignKeyAction.SetNull) [warn]
defaultUnitId column was defined as
val defaultUnitId: Rep[Option[Int]] = column[Option[Int]]("default_unit_id", O.Default(None))
Table class, and the foreign key this column pointed to was in another
Table that had the id defined as
val unitId: Rep[Int] = column[Int]("unit_id", O.AutoInc, O.PrimaryKey)
Hindsight is twenty twent, so of course looking at this now I realize the
difference between the two types and why the implicit was being called.
However, it didn't click for me until I saw the definition of the
foreignKey method here. You'll note the types of the inputs, namely
sourceColumns: P and
targetColumns: (TT) ⇒ P. The reason the
implicit was being called was because my
Table that the
unitId was defined in was
Rep[Int]. Obvious right?
So, how do you fix this? Simple, call the
.? explicitly like so:
lazy val defaultUnitIdFk = foreignKey("fk_my_exciting_fk_constraintname", defaultUnitId, UnitTable.Unit)(u => u.unitId.?, onUpdate = ForeignKeyAction.SetNull, onDelete = ForeignKeyAction.SetNull)
Where the only change is
u => u.unitId.? instead of
u => u.unitId.
While this may seem obvious having just had it explained, if all you have
to go on is the
^ in the warning from sbt pointing to the end of the
statement. It's hard to determine what in that statement was the source
of the problem that caused an implicit. So I hope this helps people out
there who stumble on the same issue.