Scala Play: Implement custom QueryStringBindable with an optional field

Question

I'm using Scala with Play framework (2.8.1) and have a Sort class for capturing sort based query string parameters. Sample url: http://myurl:9000?sortBy=name&sortOrder=asc. Here, the sortOrder field is optional and will have default value of "asc" if nothing is provided. I have implemented own QueryStringBindable class as below:

object Sort {
  val asc = "asc"
  implicit def queryStringBinder(implicit stringBinder: QueryStringBindable[String]) = new QueryStringBindable[Sort] {
    override def bind(key: String, params: Map[String, Seq[String]]): Option[Either[String, Sort]] = {
      for {
        sortBy <- stringBinder.bind("sortBy", params)
        if(params.contains("sortOrder")) {sortOrder <- stringBinder.bind("sortOrder", params)}
      } yield {
        (sortBy, sortOrder) match {
          case (Right(sortBy), Right(sortOrder)) => Right(Sort(sortBy, Some(sortOrder)))
          case _ => Left("Unable to bind Sort")
        }
      }
    }
    override def unbind(key: String, sort: Sort): String = {
      stringBinder.unbind("sortBy", sort.sortBy) + "&" + stringBinder.unbind("sortOrder", sort.sortOrder.getOrElse(asc))
    }
  }
}

case class Sort(sortBy: String, sortOrder: Option[String] = Some(Sort.asc))

However, I'm unable to capture optional field sortOrder with default value if nothing is provided in the query string of url. I would want http://myurl:9000?sortBy=name to still sort by ascending order (default) even if &sortOrder isn't provided.

Jeffrey Chung Jeffrey Chung · Accepted Answer · 2020-06-23T20:41:35

It might be easier not to use a for comprehension:

object Sort {
  val asc = "asc"

  implicit def queryStringBinder(implicit stringBinder: QueryStringBindable[String]) = new QueryStringBindable[Sort] {
    override def bind(key: String, params: Map[String, Seq[String]]): Option[Either[String, Sort]] = {
      val sortBy = stringBinder.bind("sortBy", params) // Option[Either[String, String]]
      val sortOrder = stringBinder.bind("sortOrder", params) // Option[Either[String, String]]

      val result = // Either[String, Sort]
        (sortBy, sortOrder) match {
          case (Some(Right(field)), Some(Right(order))) => Right(Sort(field, Some(order)))
          case (Some(Right(field)), None) => Right(Sort(field))
          case _ => Left("Unable to bind Sort")
        }
      Option(result)
    }

    override def unbind(key: String, sort: Sort): String = {
      stringBinder.unbind("sortBy", sort.sortBy) + "&" + stringBinder.unbind("sortOrder", sort.sortOrder.getOrElse(asc))
    }
  }
}

case class Sort(sortBy: String, sortOrder: Option[String] = Some(Sort.asc))

Scala Play: Implement custom QueryStringBindable with an optional field

1 Answers