Package org.apache.pekko.persistence.typed.javadsl

Class EventSourcedBehavior<Command,Event,State>

java.lang.Object
org.apache.pekko.actor.typed.Behavior<T>
org.apache.pekko.actor.typed.internal.BehaviorImpl.DeferredBehavior<Command>
org.apache.pekko.persistence.typed.javadsl.EventSourcedBehavior<Command,Event,State>
Direct Known Subclasses:
EventSourcedBehaviorWithEnforcedReplies, ReplicatedEventSourcedBehavior
public abstract class EventSourcedBehavior<Command,Event,State> extends BehaviorImpl.DeferredBehavior<Command>

  • Constructor Details

    • EventSourcedBehavior

      public EventSourcedBehavior(PersistenceId persistenceId)
      Parameters:
      persistenceId - stable unique identifier for the event sourced behavior

    • EventSourcedBehavior

      public EventSourcedBehavior(PersistenceId persistenceId, BackoffSupervisorStrategy onPersistFailure)
      If using onPersistFailure the supervision is only around the event sourced behavior not any outer setup/withTimers block. If using restart any actions e.g. scheduling timers, can be done on the PreRestart signal or on the RecoveryCompleted signal.

      Parameters:
      persistenceId - stable unique identifier for the event sourced behavior
      onPersistFailure - BackoffSupervisionStrategy for persist failures

  • Method Details

    • Effect

      protected final EffectFactories<Event,State> Effect()
      Factory of effects.

      Return effects from your handlers in order to instruct persistence on how to act on the incoming message (i.e. persist events).

    • apply

      public Behavior<Command> apply(TypedActorContext<Command> context)
      INTERNAL API: DeferredBehavior init, not for user extension
      Specified by:
      apply in class BehaviorImpl.DeferredBehavior<Command>

    • commandHandler

      protected abstract CommandHandler<Command,Event,State> commandHandler()
      Implement by handling incoming commands and return an Effect() to persist or signal other effects of the command handling such as stopping the behavior or others.

      Use newCommandHandlerBuilder() to define the command handlers.

      The command handlers are only invoked when the actor is running (i.e. not replaying). While the actor is persisting events, the incoming messages are stashed and only delivered to the handler once persisting them has completed.

    • emptyState

      protected abstract State emptyState()
      Implement by returning the initial empty state object. This object will be passed into this behaviors handlers, until a new state replaces it.

      Also known as "zero state" or "neutral state".

    • eventAdapter

      public EventAdapter<Event,?> eventAdapter()
      Transform the event in another type before giving to the journal. Can be used to wrap events in types Journals understand but is of a different type than Event.

    • eventHandler

      protected abstract EventHandler<State,Event> eventHandler()
      Implement by applying the event to the current state in order to return a new state.

      Use newEventHandlerBuilder() to define the event handlers.

      The event handlers are invoked during recovery as well as running operation of this behavior, in order to keep updating the state state.

      For that reason it is strongly discouraged to perform side-effects in this handler; Side effects should be executed in thenRun or recoveryCompleted blocks.

    • journalPluginConfig

      public Optional<com.typesafe.config.Config> journalPluginConfig()
      Override and define the journal plugin config that this actor should use instead of the default.

    • journalPluginId

      public String journalPluginId()
      Override and define the journal plugin id that this actor should use instead of the default.

    • lastSequenceNumber

      public final long lastSequenceNumber(ActorContext<?> ctx)
      The last sequence number that was persisted, can only be called from inside the handlers of an EventSourcedBehavior

    • newCommandHandlerBuilder

      protected CommandHandlerBuilder<Command,Event,State> newCommandHandlerBuilder()
      Returns:
      A new, mutable, command handler builder

    • newEventHandlerBuilder

      protected final EventHandlerBuilder<State,Event> newEventHandlerBuilder()
      Returns:
      A new, mutable, event handler builder

    • newSignalHandlerBuilder

      protected final SignalHandlerBuilder<State> newSignalHandlerBuilder()
      Returns:
      A new, mutable signal handler builder

    • persistenceId

      public PersistenceId persistenceId()

    • recovery

      public Recovery recovery()
      Override to change the strategy for recovery of snapshots and events. By default, snapshots and events are recovered.

    • retentionCriteria

      public RetentionCriteria retentionCriteria()
      Criteria for retention/deletion of snapshots and events. By default, retention is disabled and snapshots are not saved and deleted automatically.

    • shouldSnapshot

      public boolean shouldSnapshot(State state, Event event, long sequenceNr)
      Initiates a snapshot if the given predicate evaluates to true.

      Decide to store a snapshot based on the State, Event and sequenceNr when the event has been successfully persisted.

      When persisting multiple events at once the snapshot is triggered after all the events have been persisted.

      Snapshots triggered by snapshotWhen will not trigger deletes of old snapshots and events if EventSourcedBehavior.retentionCriteria with RetentionCriteria.snapshotEvery is used together with shouldSnapshot. Such deletes are only triggered by snapshots matching the numberOfEvents in the RetentionCriteria.

      Returns:
      true if snapshot should be saved at the given state, event and sequenceNr when the event has been successfully persisted

    • signalHandler

      protected SignalHandler<State> signalHandler()
      Override to react on general lifecycle signals and persistence specific signals (subtypes of pekko.persistence.typed.EventSourcedSignal).

      Use newSignalHandlerBuilder() to define the signal handler.

    • snapshotAdapter

      public SnapshotAdapter<State> snapshotAdapter()
      Transform the state into another type before giving it to and from the journal. Can be used to migrate from different state types e.g. when migration from PersistentFSM to Typed EventSourcedBehavior.

    • snapshotPluginConfig

      public Optional<com.typesafe.config.Config> snapshotPluginConfig()
      Override and define the snapshot store plugin config that this actor should use instead of the default.

    • snapshotPluginId

      public String snapshotPluginId()
      Override and define the snapshot store plugin id that this actor should use instead of the default.

    • tagsFor

      public Set<String> tagsFor(Event event)
      The tagger function should give event tags, which will be used in persistence query