Sangria: How to handle custom types

Question

trying work with Sangria and Slick. New to both of them.

I have bunch of tables which share a list of common fields. Slick's representation of this is below:

case class CommonFields(created_by: Int = 0, is_deleted: Boolean = false)

trait CommonModel {
  def commonFields: CommonFields
  def created_by = commonFields.created_by
  def is_deleted = commonFields.is_deleted
}

case class User(id: Int,
                name: String,
                commonFields: CommonFields = CommonFields()) extends CommonModel

Slick tables:

  abstract class CommonTable [Model <: CommonModel] (tag: Tag, tableName: String) extends Table[Model](tag, tableName) {
    def created_by = column[Int]("created_by")
    def is_deleted = column[Boolean]("is_deleted")
  }

  case class CommonColumns(created_by: Rep[Int], is_deleted: Rep[Boolean])

  implicit object CommonShape extends CaseClassShape(
    CommonColumns.tupled, CommonFields.tupled
  )

  class UsersTable(tag: Tag) extends CommonTable[User](tag, "USERS") {
    def id = column[Int]("ID", O.PrimaryKey, O.AutoInc)
    def name = column[String]("NAME")

    def * = (id,
      name,
      CommonColumns(created_by, is_deleted)) <> (User.tupled, User.unapply)
  }

  val Users = TableQuery[UsersTable]

The problem is with Graphql:

 lazy val UserType: ObjectType[Unit, User] = deriveObjectType[Unit, User]()

When I try to create UserType using derivedObjectType Macro, it complains that

Can't find suitable GraphQL output type for .CommonFields. If you have defined it already, please consider making it implicit and ensure that it's available in the scope.

[error] lazy val UserType: ObjectType[Unit, User] = deriveObjectType[Unit, User](

How do I tell Sangria/Graphql how to handle this nested list of fields (from CommonFields) ?

Please help.

Answer 1

You are deriving the Type for User but user also has CommonFields which you have not derived. So it's not able to find Type information for CommonFields. Derive both and make the derivation implicit for CommonFields.

implicit val CommonFieldsType: ObjectType[Unit, CommonFields] = deriveObjectType[Unit, CommonFields]     
implicit val UserType: ObjectType[Unit, User] = deriveObjectType[Unit, User]