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Document using an EventSourcedBehavior as a PersistentFSM (#27931)

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Re-uses the code from the migration guide as the mgiration logic
is in adapters.

Almost seems very obvious you can do this but can't hurt to have.

* Apply suggestions from code review

Co-Authored-By: Helena Edelson <helena@users.noreply.github.com>
This commit is contained in:
Christopher Batey 2019-10-15 11:22:14 +01:00 • committed by Patrik Nordwall
parent 46fcca5f39
commit b5eb18a033
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akka-docs/src/main/paradox/typed/index-persistence.md
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@ -12,6 +12,7 @@ project.description: Event Sourcing with Akka Persistence enables actors to pers
* [persistence-style](persistence-style.md)
* [persistence-snapshot](persistence-snapshot.md)
* [persistence-testing.md](persistence-testing.md)
* [persistence-fsm.md](persistence-fsm.md)
* [persistence-schema-evolution](../persistence-schema-evolution.md)
* [persistence-query](../persistence-query.md)
* [persistence-query-leveldb](../persistence-query-leveldb.md)

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akka-docs/src/main/paradox/typed/persistence-fsm.md Normal file
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# EventSourced behaviors as finite state machines
An @apidoc[EventSourcedBehavior] can be used to represent a persistent FSM. If you're migrating an existing classic
persistent FSM to EventSourcedBehavior see the @ref[migration guide](../persistence-fsm.md#migration-to-eventsourcedbehavior).
To demonstrate this consider an example of a shopping application. A customer can be in the following states:
* Looking around
* Shopping (has something in their basket)
* Inactive
* Paid
Scala
: @@snip [PersistentFsmToTypedMigrationSpec.scala](/akka-persistence-typed/src/test/scala/docs/akka/persistence/typed/PersistentFsmToTypedMigrationSpec.scala) { #state }
Java
: @@snip [PersistentFsmToTypedMigrationCompileOnlyTest.java](/akka-persistence-typed/src/test/java/jdocs/akka/persistence/typed/PersistentFsmToTypedMigrationCompileOnlyTest.java) { #state }
And the commands that can result in state changes:
* Add item
* Buy
* Leave
* Timeout (internal command to discard abandoned purchases)
And the following read only commands:
* Get current cart
Scala
: @@snip [PersistentFsmToTypedMigrationSpec.scala](/akka-persistence-typed/src/test/scala/docs/akka/persistence/typed/PersistentFsmToTypedMigrationSpec.scala) { #commands }
Java
: @@snip [PersistentFsmToTypedMigrationCompileOnlyTest.java](/akka-persistence-typed/src/test/java/jdocs/akka/persistence/typed/PersistentFsmToTypedMigrationCompileOnlyTest.java) { #commands }
The command handler of the EventSourcedBehavior is used to convert the commands that change the state of the FSM
to events, and reply to commands.
@scala[The command handler:]@java[The `forStateType` command handler can be used:]
Scala
: @@snip [PersistentFsmToTypedMigrationSpec.scala](/akka-persistence-typed/src/test/scala/docs/akka/persistence/typed/PersistentFsmToTypedMigrationSpec.scala) { #command-handler }
Java
: @@snip [PersistentFsmToTypedMigrationCompileOnlyTest.java](/akka-persistence-typed/src/test/java/jdocs/akka/persistence/typed/PersistentFsmToTypedMigrationCompileOnlyTest.java) { #command-handler }
The event handler is used to change state once the events have been persisted. When the EventSourcedBehavior is restarted
the events are replayed to get back into the correct state.
Scala
: @@snip [PersistentFsmToTypedMigrationSpec.scala](/akka-persistence-typed/src/test/scala/docs/akka/persistence/typed/PersistentFsmToTypedMigrationSpec.scala) { #event-handler }
Java
: @@snip [PersistentFsmToTypedMigrationCompileOnlyTest.java](/akka-persistence-typed/src/test/java/jdocs/akka/persistence/typed/PersistentFsmToTypedMigrationCompileOnlyTest.java) { #event-handler }