Managing MappedColumnType conversions in a slick 3 project - scala

Question

I am trying to build custom database column converters for a new Slick 3 project. It's pretty easy to make these using the MappedColumnType, but you have to have imported the driver api. For a one-off type in a single DAO class, this is straight forward. But I would like to use my custom column types across all my DAO objects. I have been unable to construct my import in a way that the compiler can recognize the implicits.
Here is an example of the type of library I would like to construct. It has a single converter, very similar to the ubiquitous Joda date converter seen in many Slick 2 examples.
package dao
import java.sql.Date
import data.Timestamp
import play.api.db.slick.{DatabaseConfigProvider, HasDatabaseConfigProvider}
import slick.driver.JdbcProfile
case class StandardConversions(protected val dbConfigProvider: DatabaseConfigProvider)
extends HasDatabaseConfigProvider[JdbcProfile] {
import driver.api._
implicit val timestampColumnType = MappedColumnType.base[Timestamp, Date](
{ data => new Date(data.value) },
{ sql => Timestamp(sql.getTime) }
)
}
In the DAO class I try doing the import like this:
val conversions = StandardConversions(dbConfigProvider)
import conversions._
The compiler error is the familiar:
could not find implicit value for parameter tt: slick.ast.TypedType[data.Timestamp]
I'm basically stuck in dependency injection, implicit hell. Has anybody come up with a good way to maintain their custom conversions in Slick 3? Please share.

Answer 1

This is where traits come in handy:
package dao
import java.sql.Date
import data.Timestamp
import play.api.db.slick.HasDatabaseConfig
import slick.driver.JdbcProfile
trait StandardConversions extends HasDatabaseConfigProvider[JdbcProfile] {
import driver.api._
implicit val timestampColumnType = MappedColumnType.base[Timestamp, Date](
{ data => new Date(data.value) },
{ sql => Timestamp(sql.getTime) }
)
}
And then simply extend from this trait in your DAOs:
class SomeDAO #Inject()(protected val dbConfigProvider: DatabaseConfigProvider)
extends HasDatabaseConfigProvider[JdbcProfile]
with StandardConversions {
import driver.api._
// all implicits of StandardConversions are in scope here
}

Answer 2

In combination with Roman's solution, you should probably add the following import:
import play.api.libs.concurrent.Execution.Implicits.defaultContext