deferOpt

26.08.2023 — Code, Scala, Sangria, Backend — 1 min read

The problem

I might have an Id of something Option[x], if it's there, fetch it!, otherwise don't

The solution

Use DeferOpt

Here's an example

import sangria.execution.deferred.Deferred
import sangria.macros.derive._
import sangria.schema._

// Assume you have a simple data model
case class Book(id: Int, title: String)

object BookData {
  private val books = List(
    Book(1, "Book 1"),
    Book(2, "Book 2"),
    Book(3, "Book 3")
  )

  def getBookById(id: Int): Option[Book] = books.find(_.id == id)
}

// Define a GraphQL schema
val BookType = deriveObjectType[Unit, Book]()

val QueryType = ObjectType(
  "Query",
  fields[Unit, Unit](
    Field("book", OptionType(BookType),
      arguments = List(Argument("id", IntType)),
      resolve = ctx => DeferredValue(BookData.getBookById(ctx.args.arg[Int]("id")))
    )
  )
)

val schema = Schema(QueryType)

// Now you can use `deferOpt` in your query
val query =
  graphql"""
    query {
      book(id: 1) @deferOpt {
        title
      }
    }
  """

// Resolve the query
import sangria.execution.{Executor, QueryAnalysisError}

val result = Executor.execute(schema, query, deferredResolver = sangria.execution.deferred.DeferOptResolver.fetchDeferred)

// Print the result
import scala.concurrent.Await
import scala.concurrent.duration._

val eventualResult = result.map(_.toString)
val resultString = Await.result(eventualResult, 5.seconds)
println(resultString)