How to implement an implicit Write for an Object in Play - scala

Question

I have a model
package models
import scala.slick.driver.SQLServerDriver.simple._
import play.api.libs.json._
import play.api.db.DB
import play.api.Play.current
import Database.threadLocalSession
case class College(collegeCode: String, collegeName: String)
object College {
lazy val database = Database.forDataSource(DB.getDataSource())
val CollegeTable = new Table[College]("College"){
def collegeCode = column[String]("CollegeCode", O.PrimaryKey)
def collegeName = column[String]("CollegeName")
def * = collegeCode ~ collegeName <> (College.apply _, College.unapply _)
implicit val CollegeReads = Json.reads[College]
implicit val CollegeWrites = Json.writes[College]
}
def getAll: Seq[College] = {
database withSession {
val q = Query(CollegeTable)
q.list
}
}
In my controller i'm attempting to render the data as JSON.
Ok(Json.toJson(College.getAll))
When viewing the page I receive this error:
No Json deserializer found for type Seq[models.College]. Try to implement an implicit Writes or Format for this type.
I thought that defining the implicit read/write in the model would take care of this. It's not until I do something like this:
Ok(Json.toJson(College.getAll.map { c=>
(c.collegeCode, c.collegeName)
} toMap))
in the controller before JSON is actually rendered. What am I doing wrong in the implicit read/write implementation?

Answer 1

The problem is that the controller cannot see the implicits. They are hidden inside the block for defining CollegeTable.
Is there any particular reason you need the implicits in this location? If not then you could put the implicits in your controller.
If you want your model to have the implicits beside it, then move the implicits up a level and import them in the controller.
object College {
implicit val CollegeReads = Json.reads[College]
implicit val CollegeWrites = Json.writes[College]
}
class Controller extends Controller {
import College.CollegeReads
import College.CollegeWrites
...
}