with spring boot, lateinit on nullable type

[zzazang]

I'm implementing lateinit in model to use DataLoader in Spring.

Refererd this example code,

graphql-kotlin/examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/model/DataLoaderQueryModel.kt

Line 5 in cb9a78f

data class Employee(

graphql-kotlin/examples/spring/src/main/kotlin/com/expediagroup/graphql/examples/execution/CustomDataFetcherFactoryProvider.kt

Line 47 in fc97f67

springDataFetcherFactory

The question is, If the lateinit is EMPTY, the value cannot be null because of "lateinit". What can be a good design for nullable field with dataloader and datafetcher?

[dariuszkuc]

Disclaimer: I'm not an expert on dataloader as I haven't used it but below should work.

Instead of a lateinit property which as you mentioned cannot be null, you should be able to expose nullable GraphQL field through a function that accepts the DataFetchingEnvironment and use that to access the dataloader, e.g.

fun foo(id: Int, environment: DataFetchingEnvironment): CompletableFuture<String?> {
  return environment.getDataLoader<Int, String?>("myDataLoader")
      .load(id)
}

[adamlarsonlee]

Bring out your dead!

Using the beautiful answer from @dariuszkuc, I implemented this pattern to allow for more easy integration of one field into multiple fields:

@Configuration
class DataLoaderConfiguration(private val accountStatusDataLoader: AccountStatusDataLoader) {

    @Bean
    fun dataLoaderRegistryFactory(): DataLoaderRegistryFactory {
        return object : DataLoaderRegistryFactory {
            override fun generate(): DataLoaderRegistry {
                val registry = DataLoaderRegistry()
                registry.register(AccountStatusDataLoader.name, accountStatusDataLoader.getLoader())
                return registry
            }
        }
    }
}


@Component
class AccountStatusDataLoader(private val accountStatusDao: AccountStatusDao) {
    companion object {
        const val name = "AccountStatusDataLoader"
    }

    fun getLoader(): DataLoader<Long, AccountStatus> =
        DataLoader.newMappedDataLoader { ids ->
             CompletableFuture.supplyAsync {
                 ids.associateWith { accountStatusDao.getById(it) }
             }
         }
}

interface AccountStatusEdge {
    val accountStatusId: Long

    fun accountStatus(environment: DataFetchingEnvironment): CompletableFuture<AccountStatus?> {
        return environment.getDataLoader<Long, AccountStatus?>(AccountStatusDataLoader.name).load(accountStatusId)
    }
}

data class Account (
    val accountId: Long,
    override val accountStatusId: Long,
) : AccountStatusEdge