# Interop

If you prefer using Cats Effect (opens new window) or Monix (opens new window) rather than ZIO, you can use the respective caliban-cats and caliban-monix modules.

The caliban-tapir module allows converting your Tapir (opens new window) endpoints into a GraphQL API.

# Cats Effect

You first need to import caliban.interop.cats.implicits._ and have an implicit zio.Runtime in scope. Then a few helpers are available:

  • the GraphQL object is enriched with interpreterAsync, a variant of interpreter that return an F[_]: Async instead of a ZIO.
  • the GraphQLInterpreter object is enriched with executeAsync and checkAsync, variants of execute and check that return an F[_]: Async instead of a ZIO.
  • the Http4sAdapter also has a helper to turn endpoints into cats-effect named convertHttpEndpointToF.

In addition to that, a Schema for any F[_]: Async: Dispatcher is provided. That means you can include fields with results wrapped in F in your queries, mutations or subscriptions.

There are two type classes responsible for the conversion between effects: caliban.interop.cats.ToEffect and caliban.interop.cats.FromEffect. The instances are derived implicitly when Async[F], Dispatcher[F], and Runtime[R] are available in the implicit scope.

# Interop with cats.effect.IO

The following example shows how to create an interpreter and run a query while only using Cats IO.

import caliban.GraphQL.graphQL
import caliban.RootResolver
import caliban.interop.cats.implicits._
import cats.effect.{ ExitCode, IO, IOApp }
import cats.effect.std.Dispatcher
import zio.Runtime

object ExampleCatsInterop extends IOApp {

  implicit val zioRuntime = Runtime.default

  case class Queries(numbers: List[Int], randomNumber: IO[Int])

  val queries = Queries(List(1, 2, 3, 4), IO(scala.util.Random.nextInt()))

  val query = """
  {
    numbers
    randomNumber
  }"""

  override def run(args: List[String]): IO[ExitCode] =
    Dispatcher[IO].use { implicit dispatcher => // required for a derivation of the schema
      val api = graphQL(RootResolver(queries))

      for {
        interpreter <- api.interpreterAsync[IO]
        result      <- interpreter.executeAsync[IO](query)
        _           <- IO(println(result.data))
      } yield ExitCode.Success
    }
}

You can find this example within the examples (opens new window) project.

# Interop with contextual effect (e.g. Kleisli)

CatsInterop (the combination of ToEffect and FromEffect) allows sharing a context between cats-effect and ZIO:

import cats.data.Kleisli
import cats.effect.IO
import cats.effect.std.Dispatcher
import caliban.interop.cats.CatsInterop
import zio.RIO

trait Context
type Effect[A] = Kleisli[IO, Context, A]

implicit val dispatcher: Dispatcher[Effect] = ???
implicit val runtime: Runtime[Context] = ???

val interop: CatsInterop.Contextual[Effect, Context] = CatsInterop.contextual(dispatcher)

val rio: RIO[Context, Int] = ???
val ce: Kleisli[IO, Context, Int] = ???

val fromRIO: Kleisli[IO, Context, Int] = interop.toEffect(rio)
val fromCE: RIO[Context, Int] = interop.fromEffect(ce)
import caliban.GraphQL.graphQL
import caliban.{ GraphQL, RootResolver }
import caliban.interop.cats._
import caliban.interop.cats.implicits._
import caliban.schema.GenericSchema
import cats.data.Kleisli
import cats.effect.{ Async, ExitCode, IO, IOApp }
import cats.effect.std.Dispatcher
import cats.effect.std.Console
import cats.syntax.flatMap._
import cats.syntax.functor._
import cats.mtl.Local
import cats.mtl.syntax.local._
import zio.Runtime

object Simple extends IOApp {

  case class Queries[F[_]](numbers: List[Int], randomNumber: F[Int])

  val query = """
  {
    numbers
    randomNumber
  }"""

  case class TraceId(value: String)

  type TraceLocal[F[_]] = Local[F, TraceId]

  trait Logger[F[_]] {
    def info(message: String): F[Unit]
  }

  def program[F[_]: Async](implicit
    logger: Logger[F],
    local: Local[F, TraceId],
    inject: InjectEnv[F, TraceId],
    runtime: Runtime[TraceId]
  ): F[ExitCode] =
    Dispatcher[F].use { implicit dispatcher => 
      implicit val interop: CatsInterop.Contextual[F, TraceId] = CatsInterop.contextual(dispatcher) // required for a derivation of the schema
      
      val genRandomNumber = logger.info("Generating number") >> Async[F].delay(scala.util.Random.nextInt())

      val queries = Queries(
        List(1, 2, 3, 4),
        genRandomNumber.scope[TraceId](TraceId("gen-number"))
      )

      val api: GraphQL[TraceId] = {
        val schema: GenericSchema[TraceId] = new GenericSchema[TraceId] {}
        import schema._

        graphQL(RootResolver(queries))
      }

      for {
        interpreter <- api.interpreterAsync[F]
        result      <- interpreter.executeAsync[F](query)
        _           <- logger.info(result.data.toString)
      } yield ExitCode.Success
    }

  override def run(args: List[String]): IO[ExitCode] = {
    type Effect[A] = Kleisli[IO, TraceId, A]

    val root = TraceId("root")

    implicit val runtime = Runtime.default.as(root)
    implicit val logger  = new Logger[Effect] {
      def info(message: String): Effect[Unit] =
        for {
          traceId <- Local[Effect, TraceId].ask[TraceId]
          _       <- Console[Effect].println(s"$message - $traceId")
        } yield ()
    }

    program[Effect].run(root)
  }
}

There is another real world example (opens new window), that shows how to share auth info between cats-effect and ZIO.

# Monix (only with cats-effect 2.x)

You first need to import caliban.interop.monix.implicits._ and have an implicit zio.Runtime in scope. Then a few helpers are available:

  • the GraphQL object is enriched with interpreterAsync, a variant of interpreter that return a Monix Task instead of a ZIO.
  • the GraphQLInterpreter object is enriched with executeAsync and checkAsync, variants of execute and check that return a Monix Task instead of a ZIO.

In addition to that, a Schema for any Monix Task as well as Observable is provided.

The following example shows how to create an interpreter and run a query while only using Monix Task.

import caliban.GraphQL.graphQL
import caliban.RootResolver
import caliban.interop.monix.implicits._
import cats.effect.ExitCode
import monix.eval.{ Task, TaskApp }
import monix.execution.Scheduler
import zio.Runtime

object ExampleMonixInterop extends TaskApp {

  implicit val zioRuntime = Runtime.default
  implicit val monixScheduler: Scheduler = scheduler

  case class Queries(numbers: List[Int], randomNumber: Task[Int])

  val queries     = Queries(List(1, 2, 3, 4), Task.eval(scala.util.Random.nextInt()))
  val api = graphQL(RootResolver(queries))

  val query = """
  {
    numbers
    randomNumber
  }"""

  override def run(args: List[String]): Task[ExitCode] =
    for {
      interpreter <- api.interpreterAsync
      result      <- interpreter.executeAsync(query)
      _           <- Task.eval(println(result.data))
    } yield ExitCode.Success
}

You can find this example within the examples (opens new window) project.

# Tapir

After adding the caliban-tapir dependency to your build, adding import caliban.interop.tapir._ to your code will introduce an extension method called toGraphQL on Tapir's Endpoint and ServerEndpoint. This method will convert your endpoint into a GraphQL object that you can then combine and expose.

The conversion rules are the following:

  • GET endpoints are turned into Queries
  • PUT, POST and DELETE endpoints are turned into Mutations
  • fixed query paths are used to name GraphQL fields (e.g. an endpoint /book/add will give a GraphQL field named bookAdd)
  • query parameters, headers, cookies and request body are used as GraphQL arguments
  • there should be an implicit Schema for both the input and the output types and an implicit ArgBuilder for the input type (see the dedicated docs)

Let's look at an example. Imagine we have the following Tapir endpoint:

import io.circe.generic.auto._
import sttp.tapir._
import sttp.tapir.generic.auto._
import sttp.tapir.json.circe._

case class Book(title: String, year: Int)

val addBook: PublicEndpoint[(Book, String), Nothing, Unit, Any] =
  infallibleEndpoint
    .post
    .in("books")
    .in("add")
    .in(
      jsonBody[Book]
        .description("The book to add")
        .example(Book("Pride and Prejudice", 1813))
    )
    .in(header[String]("X-Auth-Token").description("The token is 'secret'"))

And a possible implementation:

import zio.UIO

def bookAddLogic(book: Book, token: String): UIO[Unit] = ???

Just like you can create an http4s route by calling toRoute and passing an implementation, call toGraphQL to create a GraphQL API:

import caliban.GraphQL
import caliban.interop.tapir._ // summons 'toGraphQL' extension

val api: GraphQL[Any] = addBook.toGraphQL((bookAddLogic _).tupled)

That's it! You can combine multiple GraphQL objects using |+| and expose the result using one of Caliban's adapters.

If you want to reuse bookAddLogic for both GraphQL and regular HTTP, you can turn your Endpoint into a ServerEndpoint by calling .serverLogicSuccess:

import sttp.tapir.server.ServerEndpoint

val addBookEndpoint: ServerEndpoint.Full[Unit, Unit, (Book, String), Nothing, Unit, Any, UIO] =
  addBook.serverLogicSuccess[UIO] { case (book, token) => bookAddLogic(book, token) }

This can then be used to generate both an HTTP route (e.g. toRoutes with http4s) and a GraphQL API (.toGraphQL).

val api: GraphQL[Any] = addBookEndpoint.toGraphQL

You can find a full example (opens new window) on github.

# GraphQL restrictions

GraphQL spec (opens new window) requires unique naming for all operations.

To customize the name (opens new window) of an operation use EndpointInfo.name

endpoint
  .name("overrideName")