EventSourcedOnCommandBehavior

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".

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.

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.

Implement by applying the event to the current state in order to return a new state.

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.

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).

INTERNAL API: DeferredBehavior init, not for user extension

Can be used to delete events after shouldSnapshot.

Can be used in combination with EventSourcedBehavior.retentionCriteria in a way that events are triggered up the the oldest snapshot based on RetentionCriteria.snapshotEvery config.

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.

Narrow the type of this Behavior, which is always a safe operation. This method is necessary to implement the contravariant nature of Behavior (which cannot be expressed directly due to type inference problems).

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

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

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

Events can be deleted if deleteEventsOnSnapshot returns true.

Override to react on general lifecycle signals and persistence specific signals (subtypes of akka.persistence.typed.EventSourcedSignal).

Use EventSourcedBehavior#newSignalHandlerBuilder to define the signal handler.

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.

Override to define a custom stash capacity per entity. If not defined, the default akka.persistence.typed.stash-capacity will be used.

Return tags to store for the given event and state, the tags can then be used in persistence query. The state passed to the tagger allows for toggling a tag with one event but keep all events after it tagged based on a property or the type of the state.

Return tags to store for the given event, the tags can then be used in persistence query.

If State) is overriden this method is ignored.

Transform the incoming messages by placing a funnel in front of the wrapped Behavior: the supplied PartialFunction decides which message to pull in (those that it is defined at) and may transform the incoming message to place them into the wrapped Behavior’s type hierarchy. Signals are not transformed.

Example:

val b: Behavior[Number] =
  Behaviors
    .receive[String] { (ctx, msg) =>
      println(msg)
      Behaviors.same
    }
    .transformMessages[Number] {
      case b: BigDecimal => s"BigDecimal($b)"
      case i: BigInt     => s"BigInteger($i)"
      // all other kinds of Number will be `unhandled`
    }

The ClassTag for Outer ensures that only messages of this class or a subclass thereof will be intercepted. Other message types (e.g. a private protocol) will bypass the interceptor and be continue to the inner behavior untouched.

Override and define the snapshot selection criteria used by this actor instead of the default. By default the most recent snapshot is used, and the remaining state updates are recovered by replaying events from the sequence number up until which the snapshot reached.

You may configure the behavior to skip replaying snapshots completely, in which case the recovery will be performed by replaying all events -- which may take a long time.