com.lightbend.lagom.javadsl.persistence
PersistentEntity
Related Docs:
object PersistentEntity
| package persistence
com.lightbend.lagom.javadsl.persistence
Behavior consists of current state and functions to process incoming commands and persisted events.
Behavior consists of current state and functions to process incoming commands
and persisted events. Behavior is an immutable class. Use the mutable BehaviorBuilder
for defining command and event handlers.
Mutable builder that is used for defining the event and command handlers.
Mutable builder that is used for defining the event and command handlers. Use [#build] to create the immutable Behavior.
The context that is passed to command handler function.
A command handler returns a Persist directive that defines what event or events,
if any, to persist.
A command handler returns a Persist directive that defines what event or events,
if any, to persist. Use the thenPersist, thenPersistAll or done methods of the context
that is passed to the command handler function to create the Persist directive.
The context that is passed to read-only command handlers.
Abstract method that must be implemented by concrete subclass to define the behavior of the entity.
Abstract method that must be implemented by concrete subclass to define the behavior of the entity. Use #newBehaviorBuilder to create a mutable builder for defining the behavior.
The name of this entity type.
The name of this entity type. It should be unique among the entity
types of the service. By default it is using the short class name
of the concrete PersistentEntity class. Subclass may override
to define other type names. It is needed to override and retain
the original name when the class name is changed because this name
is part of the key of the store data (it is part of the persistenceId
of the underlying PersistentActor).
Create a new empty Behavior with a given state.
Create a new empty BehaviorBuilder with a given state.
This method is called to notify the entity that the recovery process is finished.
Current state of the entity.
Current state of the entity. Typically accessed from event and command handlers.
A
PersistentEntityhas a stable entity identifier, with which it can be accessed from anywhere in the cluster. It is run by an actor and the state is persistent using event sourcing.initialBehavioris an abstract method that your concrete subclass must implement. It returns theBehaviorof the entity. The behavior consists of current state and functions to process incoming commands and persisted events.The
PersistentEntityreceives commands of typeCommandthat can be validated before persisting state changes as events of typeEvent. The functions that process incoming commands are registered in theBehaviorusingsetCommandHandlerof theBehaviorBuilder.A command may also be read-only and only perform some side-effect, such as replying to the request. Such command handlers are registered using
setReadOnlyCommandHandlerof theBehaviorBuilder. Replies are sent with thereplymethod of the context that is passed to the command handler function.A command handler returns a
Persistdirective that defines what event or events, if any, to persist. Use thethenPersist,thenPersistAllordonemethods of the context that is passed to the command handler function to create thePersistdirective.When an event has been persisted successfully the state of type
Stateis updated by applying the event to the current state. The functions for updating the state are registered with thesetEventHandlermethod of theBehaviorBuilder. The event handler returns the new state. The state must be immutable, so you return a new instance of the state. Current state can be accessed from the event handler with thestatemethod of thePersistentEntity. The same event handlers are also used when the entity is started up to recover its state from the stored events.After persisting an event, external side effects can be performed in the
afterPersistfunction that can be defined when creating thePersistdirective. A typical side effect is to reply to the request to confirm that it was performed successfully. Replies are sent with thereplymethod of the context that is passed to the command handler function.The event handlers are typically only updating the state, but they may also change the behavior of the entity in the sense that new functions for processing commands and events may be defined. This is useful when implementing finite state machine (FSM) like entities. Event handlers that change the behavior are registered with the
setEventHandlerChangingBehaviorof theBehaviorBuilder. Such an event handler returns the newBehaviorinstead of just returning the new state. You can access current behavior with thebehaviormethod of thePersistentEntityand using thebuildermethod of theBehavior.When the entity is started the state is recovered by replaying stored events. To reduce this recovery time the entity may start the recovery from a snapshot of the state and then only replaying the events that were stored after the snapshot. Such snapshots are automatically saved after a configured number of persisted events. The snapshot if any is passed as a parameter to the
initialBehaviormethod and you should use that state as the state of the returnedBehavior. One thing to keep in mind is that if you are using event handlers that change the behavior (setEventHandlerChangingBehavior) you must also restore correspondingBehaviorfrom the snapshot state that is passed as a parameter to theinitialBehaviormethod.Type parameter
Command: the super type of all commands, must implement PersistentEntity.ReplyType to define the reply type of each command type Type parameterEvent: the super type of all events Type parameterState: the type of the state