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Clarify documentation for persisting multiple events in the context o… (#30169)

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* Add details to event handler section clarifying how multiple events are handled
* Add details to side-effect section to clarify how state passed to the side-effect method is an accumulation of state changes from all persisted events
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Dave Kichler 2021-04-19 11:33:10 -04:00 • committed by GitHub
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akka-docs/src/main/paradox/typed/persistence.md
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@ -155,6 +155,7 @@ function e.g @scala[`Effect.persist(..).thenRun`]@java[`Effect().persist(..).the
### Event handler
When an event has been persisted successfully the new state is created by applying the event to the current state with the `eventHandler`.
In the case of multiple persisted events, the `eventHandler` is called with each event in the same order as they were passed to @scala[`Effect.persist(..)`]@java[`Effect().persist(..)`].
The state is typically defined as an immutable class and then the event handler returns a new instance of the state.
You may choose to use a mutable class for the state, and then the event handler may update the state instance and
@ -235,7 +236,8 @@ chain side effects that are to be performed after successful persist which is ac
function e.g @scala[`Effect.persist(..).thenRun`]@java[`Effect().persist(..).thenRun`].
In the example below the state is sent to the `subscriber` ActorRef. Note that the new state after applying
the event is passed as parameter of the `thenRun` function.
the event is passed as parameter of the `thenRun` function. In the case where multiple events have been persisted,
the state passed to `thenRun` is the updated state after all events have been handled.
All `thenRun` registered callbacks are executed sequentially after successful execution of the persist statement
(or immediately, in case of `none` and `unhandled`).