Package org.axonframework.eventsourcing.eventstore

Class SnapshotCapableEventStorageEngine

java.lang.Object

org.axonframework.eventsourcing.eventstore.SnapshotCapableEventStorageEngine

All Implemented Interfaces:

DescribableComponent, EventStorageEngine

@Internal
public class SnapshotCapableEventStorageEngine
extends Object
implements EventStorageEngine

Decorator for an EventStorageEngine that adds support for the SourcingStrategy.Snapshot sourcing strategy for stores that do not support this strategy natively.

When the given SourcingCondition carries a SourcingStrategy.Snapshot strategy, this decorator loads the latest snapshot from the given SnapshotStore and prepends it as a synthetic leading message to the event stream, followed by the events that occurred after the snapshot's position. If no snapshot is found, or if loading fails, it falls back to full event sourcing from the beginning.

All other sourcing strategies, as well as all append and streaming operations, are delegated directly to the wrapped engine.

Since:

5.1.0

Author:

John Hendrikx

Nested Class Summary

Nested classes/interfaces inherited from interface org.axonframework.eventsourcing.eventstore.EventStorageEngine

EventStorageEngine.AppendTransaction<R>

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DECORATION_ORDER	The decoration order used when registering this wrapper as a decorator for EventStorageEngine components.

Constructor Summary

Constructors

Constructor	Description
SnapshotCapableEventStorageEngine(EventStorageEngine delegate, SnapshotStore snapshotStore)	Constructs a SnapshotCapableEventStorageEngine wrapping the given delegate engine with snapshot loading capability backed by the given snapshotStore.

Method Summary

Modifier and Type	Method	Description
CompletableFuture<EventStorageEngine.AppendTransaction<?>>	appendEvents(AppendCondition condition, @Nullable ProcessingContext context, List<TaggedEventMessage<?>> events)	Appends a List of events to the underlying storage solution.
void	describeTo(ComponentDescriptor descriptor)	Describe the properties of this DescribableComponent with the given descriptor.
CompletableFuture<TrackingToken>	firstToken()	Creates a TrackingToken that is at the first position of an event stream.
CompletableFuture<TrackingToken>	latestToken()	Creates a TrackingToken that is at the latest position of an event stream.
MessageStream<EventMessage>	source(SourcingCondition condition)	Creates a finite MessageStream of events matching the given condition.
MessageStream<EventMessage>	stream(StreamingCondition condition)	Creates an infinite MessageStream of events matching the given condition.
CompletableFuture<TrackingToken>	tokenAt(Instant at)	Creates a TrackingToken that tracks all events after the given at.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.axonframework.eventsourcing.eventstore.EventStorageEngine

appendEvents

Field Details

DECORATION_ORDER

public static final int DECORATION_ORDER

The decoration order used when registering this wrapper as a decorator for EventStorageEngine components.

See Also:

• Constant Field Values

Constructor Details

SnapshotCapableEventStorageEngine

public SnapshotCapableEventStorageEngine(EventStorageEngine delegate,
 SnapshotStore snapshotStore)

Constructs a SnapshotCapableEventStorageEngine wrapping the given delegate engine with snapshot loading capability backed by the given snapshotStore.

Parameters:

delegate - the EventStorageEngine to delegate non-snapshot operations to, cannot be null

snapshotStore - the SnapshotStore used to load snapshots, cannot be null

Method Details

source

public MessageStream<EventMessage> source(SourcingCondition condition)

Description copied from interface: EventStorageEngine

Creates a finite MessageStream of events matching the given condition.

The final entry of the stream always contains a ConsistencyMarker in the MessageStream.Entry's resources, paired with a TerminalEventMessage. This ConsistencyMarker should be used to construct the AppendCondition when appending events.

The condition dictates the sequence to load based on the EventsCondition.criteria(). Additionally, an optional SourcingCondition.strategy() may be provided.

The returned stream is finite, i.e. it should not block to wait for further events if the end of the event stream of the aggregate is reached.

Specified by:

source in interface EventStorageEngine

Parameters:

condition - The SourcingCondition dictating the stream of events to source.

Returns:

A finite MessageStream of events matching the given condition.

appendEvents

public CompletableFuture<EventStorageEngine.AppendTransaction<?>> appendEvents(AppendCondition condition,
 @Nullable ProcessingContext context,
 List<TaggedEventMessage<?>> events)

Description copied from interface: EventStorageEngine

Appends a List of events to the underlying storage solution.

Events will be appended in the order that they are offered in, validating the given condition before being stored. Note that all events should have a unique event identifier. Tags paired with the events will be stored as well.

Implementations may be able to detect conflicts during the append stage. In such case, the returned completable future will complete exceptionally, indicating such conflict. Other implementations may delay such checks until the EventStorageEngine.AppendTransaction.commit() is called.

Called during the PREPARE_COMMIT phase.

Specified by:

appendEvents in interface EventStorageEngine

Parameters:

condition - The condition describing the transactional requirements for the append transaction

context - The current ProcessingContext, if any.

events - The List of events to append to the underlying storage solution.

Returns:

A transaction instance that can be committed or rolled back.

stream

public MessageStream<EventMessage> stream(StreamingCondition condition)

Description copied from interface: EventStorageEngine

Creates an infinite MessageStream of events matching the given condition.

The condition may dictate the StreamingCondition.position() to start streaming from, as well as define filter criteria for the returned MessageStream.

Specified by:

stream in interface EventStorageEngine

Parameters:

condition - The StreamingCondition dictating the StreamingCondition.position() to start streaming from, as well as the filter criteria used for the returned MessageStream.

Returns:

An infinite MessageStream of events matching the given condition.

firstToken

public CompletableFuture<TrackingToken> firstToken()

Description copied from interface: EventStorageEngine

Creates a TrackingToken that is at the first position of an event stream.

In other words, a token that tracks events from the beginning of time.

Specified by:

firstToken in interface EventStorageEngine

Returns:

A CompletableFuture of a TrackingToken at the first position of an event stream.

latestToken

public CompletableFuture<TrackingToken> latestToken()

Description copied from interface: EventStorageEngine

Creates a TrackingToken that is at the latest position of an event stream.

In other words, a token that tracks all new events from this point forward.

Specified by:

latestToken in interface EventStorageEngine

Returns:

A CompletableFuture of a TrackingToken at the latest position of an event stream.

tokenAt

public CompletableFuture<TrackingToken> tokenAt(Instant at)

Description copied from interface: EventStorageEngine

Creates a TrackingToken that tracks all events after the given at.

If there is an event exactly at the given at, it will be tracked too.

Specified by:

tokenAt in interface EventStorageEngine

Parameters:

at - The Instant determining how the TrackingToken should be created. A tracking token should point to very first event before this Instant.

Returns:

A CompletableFuture of a TrackingToken at the given at, if there aren't events matching this criteria null is returned

describeTo

public void describeTo(ComponentDescriptor descriptor)

Description copied from interface: DescribableComponent

Describe the properties of this DescribableComponent with the given descriptor.

Components should call the appropriate describeProperty methods on the descriptor to register their properties. The descriptor is responsible for determining how these properties are formatted and structured in the final output.

Best Practices: As a general rule, all relevant fields of a DescribableComponent implementation should be described in this method. However, developers have discretion to include only the fields that make sense in the context. Not every field may be meaningful for description purposes, especially internal implementation details. Furthermore, components might want to expose different information based on their current state. The final decision on what properties to include lies with the person implementing the describeTo method, who should focus on providing information that is useful for understanding the component's configuration and state.

Example implementation:

 public void describeTo(ComponentDescriptor descriptor) {
     descriptor.describeProperty("name", this.name);
     descriptor.describeProperty("enabled", this.enabled);
     descriptor.describeProperty("configuration", this.configuration); // A nested component
     descriptor.describeProperty("handlers", this.eventHandlers);      // A collection
 }
 

Specified by:

describeTo in interface DescribableComponent

Parameters:

descriptor - The component descriptor to describe this DescribableComponentn its properties in.