org.axonframework.eventsourcing

Class EventCountSnapshotTriggerDefinition

java.lang.Object

org.axonframework.eventsourcing.EventCountSnapshotTriggerDefinition

All Implemented Interfaces:

SnapshotTriggerDefinition

public class EventCountSnapshotTriggerDefinition
extends Object
implements SnapshotTriggerDefinition

Snapshotter trigger mechanism that counts the number of events to decide when to create a snapshot. A snapshot is triggered when the number of events applied on an aggregate exceeds the given threshold.

This number can exceed in two distinct scenarios:

1. When initializing / event sourcing the aggregate in question.
2. When new events are being applied by the aggregate.

If the definable threshold is met in situation one, the snapshot will be triggered regardless of the outcome of command handling. Thus also if command handling returns exceptionally. If the threshold is only reached once the aggregate has been fully initialized, than the snapshot will only be triggered if handling resolves successfully.

Since:

3.0

Author:

Allard Buijze

Constructor Summary

Constructors

Constructor and Description
EventCountSnapshotTriggerDefinition(Snapshotter snapshotter, int threshold) Initialized the SnapshotTriggerDefinition to threshold snapshots using the given snapshotter when threshold events have been applied to an Aggregate instance

Method Summary

Modifier and Type	Method and Description
SnapshotTrigger	prepareTrigger(Class<?> aggregateType) Prepares a new trigger for an aggregate with the given aggregateIdentifier and aggregateType.
SnapshotTrigger	reconfigure(Class<?> aggregateType, SnapshotTrigger trigger) Reconfigure the necessary infrastructure components in the given trigger instance, which may have been lost in the (de)serialization process.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

EventCountSnapshotTriggerDefinition

public EventCountSnapshotTriggerDefinition(Snapshotter snapshotter,
                                           int threshold)

Initialized the SnapshotTriggerDefinition to threshold snapshots using the given snapshotter when threshold events have been applied to an Aggregate instance

Parameters:

snapshotter - the snapshotter to notify when a snapshot needs to be taken

threshold - the number of events that will threshold the creation of a snapshot event

Method Detail

prepareTrigger

public SnapshotTrigger prepareTrigger(Class<?> aggregateType)

Description copied from interface: SnapshotTriggerDefinition

Prepares a new trigger for an aggregate with the given aggregateIdentifier and aggregateType. The trigger will be notified of each event applied on the aggregate, as well as the moment at which the aggregate state is fully initialized based on its historic events.

It is highly recommended that the instances returned by this method are Serializable. Any resources that the trigger needs that are not serializable, can be reattached by implementing the SnapshotTriggerDefinition.reconfigure(Class, SnapshotTrigger) method. This method is invoked when a SnapshotTrigger has been deserialized.

Specified by:

prepareTrigger in interface SnapshotTriggerDefinition

Parameters:

aggregateType - The type of aggregate for which to create a trigger

Returns:

the trigger instance for an aggregate

reconfigure

public SnapshotTrigger reconfigure(Class<?> aggregateType,
                                   SnapshotTrigger trigger)

Description copied from interface: SnapshotTriggerDefinition

Reconfigure the necessary infrastructure components in the given trigger instance, which may have been lost in the (de)serialization process.

Since implementations of the SnapshotTrigger often rely on a Snapshotter which cannot be serialized, it may be necessary to inject these resourcs after deserialization of a trigger.

Implementations returning a Serializable SnapshotTrigger (which is recommended), should implement this method if not all fields could be initialized base don serialized data.

Specified by:

reconfigure in interface SnapshotTriggerDefinition

Parameters:

aggregateType - The type of aggregate for which this trigger was created

trigger - The trigger instance formerly created using SnapshotTriggerDefinition.prepareTrigger(Class)

Returns:

a fully (re)configured trigger instance, may be the same trigger instance.