kalix.scalasdk.valueentity.ValueEntity.scala Maven / Gradle / Ivy
/*
* Copyright 2021 Lightbend Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package kalix.scalasdk.valueentity
import kalix.scalasdk.{ DeferredCall, Metadata, SideEffect }
import kalix.scalasdk.impl.valueentity.ValueEntityEffectImpl
import io.grpc.Status
object ValueEntity {
object Effect {
/**
* Construct the effect that is returned by the command handler. The effect describes next processing actions, such
* as updating state and sending a reply.
*
* @tparam S
* The type of the state for this entity.
*/
trait Builder[S] {
def updateState(newState: S): OnSuccessBuilder[S]
/**
* Delete the entity. No additional updates are allowed afterwards.
*/
def deleteEntity(): OnSuccessBuilder[S]
/**
* Delete the entity. No additional updates are allowed afterwards.
*/
@deprecated("Renamed to deleteEntity", "1.1.5")
def deleteState(): OnSuccessBuilder[S]
/**
* Create a message reply.
*
* @param message
* The payload of the reply.
* @return
* A message reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def reply[T](message: T): Effect[T]
/**
* Create a message reply.
*
* @param message
* The payload of the reply.
* @param metadata
* The metadata for the message.
* @return
* A message reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def reply[T](message: T, metadata: Metadata): Effect[T]
/**
* Create a forward reply.
*
* @param serviceCall
* The service call representing the forward.
* @return
* A forward reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def forward[T](serviceCall: DeferredCall[_, T]): Effect[T]
/**
* Create an error reply.
*
* @param description
* The description of the error.
* @return
* An error reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def error[T](description: String): Effect[T]
/**
* Create an error reply.
*
* @param description
* The description of the error.
* @param statusCode
* A gRPC status code.
* @return
* An error reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def error[T](description: String, statusCode: Status.Code): Effect[T]
}
trait OnSuccessBuilder[S] {
/**
* Reply after for example `updateState`.
*
* @param message
* The payload of the reply.
* @return
* A message reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def thenReply[T](message: T): Effect[T]
/**
* Reply after for example updateState.
*
* @param message
* The payload of the reply.
* @param metadata
* The metadata for the message.
* @return
* A message reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def thenReply[T](message: T, metadata: Metadata): Effect[T]
/**
* Create a forward reply after for example updateState.
*
* @param serviceCall
* The service call representing the forward.
* @return
* A forward reply.
* @tparam T
* The type of the message that must be returned by this call.
*/
def thenForward[T](serviceCall: DeferredCall[_, T]): Effect[T]
}
}
/**
* An Effect is a description of what Kalix needs to do after the command is handled. You can think of it as a set of
* instructions you are passing to Kalix. Kalix will process the instructions on your behalf and ensure that any data
* that needs to be persisted will be persisted.
*
* Each Kalix component defines its own effects, which are a set of predefined operations that match the capabilities
* of that component.
*
* A ValueEntity Effect can either:
*
* - update the entity state and send a reply to the caller
* - directly reply to the caller if the command is not requesting any state change
* - rejected the command by returning an error
* - instruct Kalix to delete the entity
*
* A return type to allow returning forwards or failures, and attaching effects to messages.
*
* @tparam T
* The type of the message that must be returned by this call.
*/
trait Effect[T] {
/**
* Attach the given side effects to this reply.
*
* @param sideEffects
* The effects to attach.
* @return
* A new reply with the attached effects.
*/
def addSideEffects(sideEffects: Seq[SideEffect]): Effect[T]
}
}
/**
* Value Entities persist their state on every change. You can think of them as a Key-Value entity where the key is the
* entity id and the value is the state of the entity.
*
* Kalix Value Entities have nothing in common with the domain-driven design concept of Value Objects. The Value in the
* name refers to the direct modification of the entity's state.
*
* When implementing a Value Entity, you first define what will be its internal state (your domain model), and the
* commands it will handle (mutation requests).
*
* Each command is handled by a command handler. Command handlers are methods returning an
* [[kalix.scalasdk.valueentity.ValueEntity.Effect]]. When handling a command, you use the Effect API to:
*
* - update the entity state and send a reply to the caller
* - directly reply to the caller if the command is not requesting any state change
* - rejected the command by returning an error
* - instruct Kalix to delete the entity
*
* @tparam S
* The type of the state for this entity.
*/
abstract class ValueEntity[S] {
private var _commandContext: Option[CommandContext] = None
/**
* Implement by returning the initial empty state object. This object will be passed into the command handlers, until
* a new state replaces it.
*
* Also known as "zero state" or "neutral state".
*
*
null is an allowed value.
*/
def emptyState: S
/**
* Additional context and metadata for a command handler.
*
*
It will throw an exception if accessed from constructor.
*/
protected final def commandContext(): CommandContext = {
try {
_commandContext.get
} catch {
case _: NoSuchElementException =>
throw new IllegalStateException("CommandContext is only available when handling a command.")
}
}
/** INTERNAL API */
final def _internalSetCommandContext(context: Option[CommandContext]): Unit = {
_commandContext = context
}
protected final def effects: ValueEntity.Effect.Builder[S] =
ValueEntityEffectImpl[S]()
}