Micronaut - KMongo - Jackson

Controller.kt

// Example controller

@Controller
@Validated
class DemoBeanController(
	private val service: Service // Injected by Micronaut
) {

  @Get("/{id}")
  // Micronaut 1.3 supports coroutines, this also works in earlier versions.
  fun find(@ValidObjectId id: String): CompletableFuture<DemoBean?> = CoroutineScope(Dispatchers.Default).future {
    service.findById(ObjectId(id).toId())
  }
}

KMongoFactory.kt

// Place this class somewhere in your project. Micronaut will wire this together automatically.

import com.fasterxml.jackson.databind.Module
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule
import com.mongodb.MongoClientSettings
import com.mongodb.reactivestreams.client.MongoClient
import io.micronaut.context.annotation.Factory
import io.micronaut.context.annotation.Requires
import org.bson.codecs.configuration.CodecRegistry
import org.litote.kmongo.reactivestreams.KMongo
import org.litote.kmongo.coroutine.CoroutineClient
import org.litote.kmongo.coroutine.coroutine
import org.litote.kmongo.id.jackson.IdJacksonModule
import org.litote.kmongo.service.ClassMappingType
import org.litote.kmongo.util.CollectionNameFormatter
import javax.inject.Singleton

@Factory
@Requires(classes = [KMongo::class])
class KMongoFactory {

	init {
		// KMongo: construct lower case collection names from bean classes.
		CollectionNameFormatter.useLowerCaseCollectionNameBuilder()
	}

	/**
	 * Inject KMongo's [CodecRegistry] for mapping data classes.
	 */
	@Singleton
	fun codecRegistry(): CodecRegistry = ClassMappingType.codecRegistry(MongoClientSettings.getDefaultCodecRegistry())

	/**
	 * Inject KMongo's [CoroutineClient] instead of the default [MongoClient].
	 */
	@Singleton
	fun coroutineClient(client: MongoClient): CoroutineClient = client.coroutine

	/**
	 * Jackson: convert Mongo ObjectId's to string and vice versa.
	 */
	@Singleton
	fun idJacksonModule(): Module = IdJacksonModule()

	/**
	 * Jackson: convert [java.time.LocalDate] to and from strings.
	 */
	@Singleton
	fun javaTimeJacksonModule(): Module = JavaTimeModule()

}

Service.kt

// A service that accesses a collection of DemoBean objects.

data class DemoBean(
  @BsonId
  val id: Id<DemoBean>,
  ...
)

@Singleton
class DemoBeanService(
	client: CoroutineClient, // Injected by Micronaut, defined in KMongoFactory.
	@Property(name = "mongodb.database") database: String
) {

  private val collection: CoroutineCollection<DemoBean> by lazy {
    // We can't use `getCollection<T>` on the coroutine database, because reified types are not supported on classes.
    // Therefore, get a handle to the collection via the MongoDatabase and the bean class.
    val db = client.getDatabase(database).database
      db.getCollection(KMongoUtil.defaultCollectionName(DemoBean::class), DemoBean::class.java).coroutine
    }

  suspend fun findById(id: Id<DemoBean>): DemoBean? = collection.find().first() // ...

  suspend fun save(bean: DemoBean) = collection.save(bean)
  
}

ValidObjectId.kt

// Custom validation for incoming Mongo ObjectIds

import javax.validation.Constraint
import javax.validation.Payload
import javax.validation.constraints.NotNull
import javax.validation.constraints.Pattern
import kotlin.reflect.KClass

@NotNull
@Pattern(regexp = "[a-f0-9]{24}", message = "objectid")
@Target(AnnotationTarget.FIELD, AnnotationTarget.VALUE_PARAMETER)
@Retention(AnnotationRetention.RUNTIME)
@Constraint(validatedBy = [])
annotation class ValidObjectId(val message: String = "objectid", val groups: Array<KClass<*>> = [], val payload: Array<KClass<out Payload>> = [])