Writing Schemas with Spring

In order to expose your queries, mutations, and subscriptions in the GraphQL schema create beans that implement the corresponding marker interface and they will be automatically picked up by graphql-kotlin-spring-server auto-configuration library.

data class Widget(val id: ID, val value: String)

@Component
class WidgetQuery : Query {
  fun widget(id: ID): Widget = getWidgetFromDB(id)
}

@Component
class WidgetMutation : Mutation {
  fun updateWidget(id: ID, value: String): Boolean = updateWidgetInDB(id, value)
}

@Component
class WidgetSubscription : Subscription {
  fun widgetChanges(id: ID): Publisher<Widget> = getPublisherOfUpdates(id)
}

will result in a Spring Boot reactive GraphQL web application with following schema.

schema {
  query: Query
  mutation: Mutation
  subscription: Subscription
}

type Widget {
    id: ID!
    value: String!
}

type Query {
  widget(id: ID!): Widget!
}

type Mutation {
    updateWidget(id: ID!, value: String!): Boolean!
}

type Subscription {
    widgetChanges(id: ID!): Widget!
}

Spring Beans

Since the top level objects are Spring components, Spring will automatically autowire dependent beans as normal. Refer to Spring Documentation for details.

@Component
class WidgetQuery(private val repository: WidgetRepository) : Query {
    fun getWidget(id: Int): Widget = repository.findWidget(id)
}

Spring Beans in Arguments

graphql-kotlin-spring-server provides Spring-aware data fetcher that automatically autowires Spring beans when they are specified as function arguments. @Autowired arguments should be explicitly excluded from the GraphQL schema by also specifying @GraphQLIgnore.

@Component
class SpringQuery : Query {
    fun getWidget(@GraphQLIgnore @Autowired repository: WidgetRepository, id: Int): Widget = repository.findWidget(id)
}

note

If you are using custom data fetcher make sure that you extend SpringDataFetcher instead of the base FunctionDataFetcher to keep this functionallity.

We have examples of these techniques implemented in Spring boot in the example app.