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Extra caveat around state in Java EventSourcedBehavior (#27706)

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Johan Andrén 2019-09-19 12:02:58 +02:00 • committed by Patrik Nordwall
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10
akka-docs/src/main/paradox/typed/persistence.md
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@ -39,7 +39,6 @@ Java
The first important thing to notice is the `Behavior` of a persistent actor is typed to the type of the `Command`
because this is the type of message a persistent actor should receive. In Akka Typed this is now enforced by the type system.
The event and state are only used internally.
The components that make up a EventSourcedBehavior are:
@ -48,6 +47,15 @@ The components that make up a EventSourcedBehavior are:
* `commandHandler` defines how to handle command by producing Effects e.g. persisting events, stopping the persistent actor.
* `eventHandler` returns the new state given the current state when an event has been persisted.
@@@ div { .group-java }
Note that the concrete class does not contain any fields with state like a regular POJO. All state of the
`EventSourcedBehavior` must be represented in the `State` or else they will not be persisted and therefore be
lost when the actor is stopped or restarted. Updates to the State are always performed in the eventHandler
based on the events.
@@@
Next we'll discuss each of these in detail.
### Command handler