Caliban is a functional Scala library for writing GraphQL clients and servers. In this talk, Pierre Ricadat will show how easily you can create your first GraphQL schema and expose it using the backend of your choice. He will then go well beyond that simple example and show how the library’s rich feature set can help solve challenging problems you will meet in the real world, such as telemetry, query optimization or authentication.

1. Production-ready
GraphQL with Caliban
Atlanta Scala Meetup, June 2023
Pierre Ricadat

2. Pierre Ricadat - @ghostdogpr
Tech Lead at Devsisters
Creator of Caliban and Shardcake
OSS Contributor

3. Table of Contents
A quick primer
What is Caliban?
Application Monitoring
How to add logs, traces and
metrics
Query Optimization
How to make your queries fast
Authentication
How to handle context
01
02
03
04

4. What is Caliban?
01
A quick primer

5. Caliban
Purely functional
Type safety
Purely functional
Minimal boilerplate
Great interop
Rich feature set
Scala
Scala.js
Scala Native
Scala
GraphQL
Server
GraphQL
Client

6. Model your GraphQL schema with
Scala types

7. Resolver is just a value

8. Scala types to GraphQL types
Case classes & sealed traits
Supported types Other types
Auto derivation (import)
Semi-auto derivation
(derives, given)
Int, String, List, etc
java.util.UUID, java.time
Future, ZIO, F[_]
Custom instance of
Schema typeclass

9. Derivation example

10. From resolver to interpreter

11. Use the http and json lib of your choice
http4s
zio http
akka http
play

12. Application Monitoring
02
How to add logs, traces and metrics

13. 3 phases of request processing
Transform query string
into Document ADT
Run the resolvers for that
query
Verify the Document ADT
conforms to the spec and
to the schema
Parsing Validation Execution

14. Introducing wrappers
Overall Wrapper
Wrap the whole query
processing
Parsing Wrapper
Wrap the parsing
phase
Validation Wrapper
Wrap the validation
phase
Execution Wrapper
Wrap the execution
phase
Field Wrapper
Wrap each individual field
execution
Introspection Wrapper
Wrap only introspection
queries

15. What’s a wrapper?

16. Simple wrapper for printing errors

17. Pre-defined wrappers
Validation
maxDepth, maxFields,
maxCost, queryCost,
timeout
Logging
printErrors,
printSlowQueries,
logSlowQueries
Telemetry
metrics, traced
Apollo Tracing Apollo Caching Apollo Persisted Queries

18. Using wrappers

19. Query Optimization
03
How to make your queries fast

20. Possible approaches
Build queries that
match the client
requests exactly
Build efficient queries
despite the nesting (n+1
query problem)
Field metadata
ZQuery
01 02

21. Do I need to query everything?

22. Laziness to the rescue!

23. The n+1 problem

24. Replacing ZIO by ZQuery

25. Defining a DataSource

26. What you get
Deduplication
If the same ID is requested
multiple times in your GraphQL
query, it will be queried from
your data source only once
Batching
Query all the needed data
at once in a single request
to your data source
Parallelism Control
Decide what can be done in
parallel and what should be
done sequentially

27. Do I need to query all fields?

28. Access field metadata

29. What’s in Field?
● Field name
● Field type
● Parent type
● Inner selection <- this is particularly useful to build SQL queries
● Arguments
● Directives
● …

30. ProtoQuill Integration
https://github.com/zio/zio-protoquill#caliban-integration

31. Authentication
04
How to handle context

32. Authentication
Typical needs:
● Reject unauthenticated requests
● Access user information stored in a
“context”

33. Use ZIO environment to store a context

34. Introducing Interceptors

35. A simple interceptor that gets a
token from headers

36. Eliminate the environment

37. Interceptor use cases
Authentication & Authorization
Reject wrong queries
Inject a context that can be used
in your API (and wrappers!)
Tracing
Extract tracing information from
incoming request and inject it into
the current span
Scope & Configuration
Change the value of the current
FiberRef to locally modify the
behavior of the API

38. There’s more!
Schema stitching
and federation
Schema
comparison
Client generation
from server code
@defer support Relay support Schema reporting

39. CREDITS: This presentation template was created by Slidesgo, including
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Thanks!
Questions?
https://github.com/ghostdogpr/caliban