Skip to main content
Version: 4.x.x


Both kotlin.Array and kotlin.collections.List are automatically mapped to the GraphQL List type (for unsupported use cases see below). Type arguments provided to Kotlin collections are used as the type arguments in the GraphQL List type. Kotlin specialized classes (e.g. IntArray) representing arrays of Java primitive types without boxing overhead are also supported.

class SimpleQuery {
fun generateList(): List<Int> {
// some logic here that generates list

fun doSomethingWithIntArray(ints: IntArray): String {
// some logic here that processes array

fun doSomethingWithIntList(ints: List<Int>): String {
// some logic here that processes list

The above Kotlin class would produce the following GraphQL schema:

type Query {
generateList: [Int!]!
doSomethingWithIntArray(ints: [Int!]!): String!
doSomethingWithIntList(ints: [Int!]!): String!

Primitive Arrays

graphql-kotlin-schema-generator supports the following primitive array types without autoboxing overhead. Similarly to the kotlin.Array of objects the underlying type is automatically mapped to GraphQL List type.

Kotlin Type

The underlying GraphQL types of primitive arrays will be corresponding to the built-in scalar types or extended scalar types provided by graphql-java.

Unsupported Collection Types

Currently, the GraphQL spec only supports Lists. Therefore, even though Java and Kotlin support number of other collection types, graphql-kotlin-schema-generator only explicitly supports Lists and primitive arrays. Other collection types such as Sets (see #201) and arbitrary Map data structures are not supported out of the box. While we do not reccomend using Map or Set in the schema, they are supported with the use of the schema hooks.

override fun willResolveMonad(type: KType): KType = when (type.classifier) {
Set::class -> List::class.createType(type.arguments)
else -> type

See Discussion #1110 for more details.