GraphQL + Kotlin

This talk was given for the Kotlin Meetup group in Oslo on the 20th of August 2019. We went through a brief introduction to GraphQL and then coded up a small GraphQL endpoint using Kotlin.

Transcript

1. GRAPHQL+KOTLIN
2. ABOUT ME As a teenager, Arnab dreamt of being a standup comedian, but somehow ended up finding the world of programming instead. He can be found coding away on his mac or dancing (sometimes both at the same time). Feel free to grab him and ask him any questions you want, especially if they involve fan theories about Game of Thrones.
3. WHAT IS GRAPHQL?
4. WHAT IS IT NOT
5. IT IS NOT A GRAPH DATABASE
6. IT IS NOT A FACEBOOK THING*
7. IT IS NOT A JAVASCRIPT THING
8. GRAPHQL IS A SPEC
9. JUST LIKE ANY SPEC, IT HAS MULTIPLE IMPLEMENTATIONS
10. WE WILL BE FOCUSING ON GRAPHQL-JAVA WITH KOTLIN
11. BUT WHY GRAPHQL? CAN’T WE JUST KEEP ON USING REST?
12. GET people/1
 { “id": “1”, “name”: “Arnab Datta” } Arnab Datta THE REST WAY
13. Arnab Datta Friends: Kim, Jessica GET people/1
 { “id": “1”, “name”: “Arnab Datta”, “friends”: [“2”, “3”] } GET people/2 { “id”: “2”, “name”: “Kim”, “friends”: [“1”] } LETS EXPAND GET people/3 { “id": “1”, “name”: “Jessica”, “friends”: [“1”] }
14. Arnab Datta Friends: Kim, Jessica GET people/1
 { “id": “1”, “name”: “Arnab Datta”, “friends”: [“2”, “3”] } GET people/2 { “id”: “2”, “name”: “Kim”, “friends”: [“1”] } THE REST WAY GET people/3 { “id": “1”, “name”: “Jessica”, “friends”: [“1”] }
15. • Multiple requests for one view • What happens if the IDs provided by the first endpoint are incorrect? • No guarantee that we can access the IDs provided by the first endpoint • We are wasting bandwidth on getting the friends of people we only need the name of.
16. Arnab Datta Friends: Kim, Jessica GET personWithFriends/1
 { “id": “1”, “name”: “Arnab Datta”, “friendNames”: [“Kim”, “Jessica”] } LETS “FIX” IT
17. • Single request per view • Access problems fixed • All done…right?
18. Frontend dev: What was the name of the endpoint for people? Backend dev: /people/:id
19. Frontend dev: What was the name of the endpoint for people? Backend dev: /people/:id Frontend dev: It only supplies the friends names. I want to create a link to their friends, so I need their IDs too Backend dev: Okay, I’ll make a PR.
20. Frontend dev: What was the name of the endpoint for people? Backend dev: /people/:id Frontend dev: It only supplies the friends names. I want to create a link to their friends, so I need their IDs too Backend dev: Okay, I’ll make a PR. Frontend dev: Do you mind adding their phone numbers too? Backend dev: Okay, I’ll make a PR.
21. CAN WE DO BETTER?
22. WHAT IS A PERSON? data class Person( val name: String, val id: UUID, val friends: List<Person> )
23. WHAT IF THIS WAS ALMOST ALL THE CODE YOUR API NEEDED?*
24. HOW ABOUT ENTITIES THAT ARE SOMEWHAT SIMILAR?
25. WHAT ABOUT PETS? sealed class Pet( abstract val name: String, abstract val id: UUID, abstract fun makeSound(): String ) data class Dog(override val name: String, override val id: UUID): Pet() { override fun makeSound() = “woof” } …
26. WHAT ABOUT PETS? sealed class Pet( abstract val name: String, abstract val id: UUID, abstract fun makeSound(): String ) data class Dog(override val name: String, override val id: UUID): Pet() { override fun makeSound() = “woof” } … This can be your API code.
27. people (id: “1”) { name } Arnab Datta THE GRAPHQL WAY
28. Arnab Datta Friends: Kim, Jessica LETS EXPAND people(id: “1”) { name friends { name } }
29. LETS CODE!