Replay events - only for a single aggregate

Imported from Google Groups
1

I finally managed to replay events (I am using event sourcing and a read model) for a @ProcessingGroup. I am using axon framework V4.1 .

But what I really want to do is rebuild the read model only for one single aggregate instance (which I know by id).

So my question ist:
Is it possible to replay events for only one single aggregate?

Thanks!

Sebastian

2

I’d really like to know too.
If you ever figured out how to do this please share. I want to use this to be able to rebuild the state at a certain timestamp. Documentation says this is one of the benefits of event sourcing, but doesn’t show how to do it.

3

Hello,

The most straightforward way is to use EventStore and read the events for specific aggregate id.

package org.axonframework.eventsourcing.eventstore;

/**
 * Open an event stream containing all domain events belonging to the given {@code aggregateIdentifier}.
 * <p>
 * The returned stream is <em>finite</em>, ending with the last known event of the aggregate. If the event store
 * holds no events of the given aggregate an empty stream is returned.
4

Hi Robert,

thanks for your reply.

But what do I do after I have read the events for my aggregate?
Can I “manually” replay them?

Thanks,
Sebastian

5

If want to replay the projection for specific aggregate using built in axon ‘processor’ thing. (Ie, resetting a token), you would need to create projection handler for every aggregate. So yes, i do not think that this is currently supported with axon to ‘filter’ specific events by their aggregate id when replaying a stream of events to project some data.

6

EDIT:

Sorry, by aggregate I’ve meant aggregate instance.

7

Hi,
Thank you for pointing me towards the EventStore#readEvents method.
My query handler was able to use the axon AnnotationEventHandlerAdapter to call my own object with @EventHandler methods to play back the events for a specific object and rebuild a state I’m interested in.
I can also filter the event stream based on timestamps, so I can do temporal queries.
I have noticed that calling readEvents without a sequence number will use snapshots. And passing ‘0’ as sequence number will play back all events. So that’s very useful.
I hope this extra information is useful to Sebastian.

Thanks again!

8

Ok thanks for all the feedback.

I managed to load the events for the one aggregate I wanted to update und also managed to replay them manually with my “Updater” class (the class with the “@ProcessingGroup” annotation). For every existing event type I had to an “if instance of XXEvent” and then call the appropriate method. Works but it’s not very nice. I might work out a more elegant solution.