axon 4 snapshot in demand

Question

I work with spring boot and axon example, i implement the snapshot feature, with the below code is working fine, after 3 events i found the data in the table snapshot_event_entry in the database

@Configuration
@AutoConfigureAfter(value = { AxonAutoConfiguration.class })
public class AxonConfig {

    @Bean
    public SnapshotTriggerDefinition catalogSnapshotTrigger(Snapshotter snapshotter) {
        return new EventCountSnapshotTriggerDefinition(snapshotter, 3);
    }
}


@Aggregate(snapshotTriggerDefinition = "catalogSnapshotTrigger")
public class CatalogAggregate { }

My question, is there a method to do a snapshot in demand? That means i want to implement an api to do the snapshot, not automatically after 3 events

Answer 1

there is nothing already in place. One way to implement what you need is to create a dedicated Command, eg PerformShapshotCmd, that will carry the aggregateId information, and a @CommandHandler into your Aggregate. You could then let Spring autowire the Snapshotter instance bean, and call for the scheduleSnapshot(Class<?> aggregateType, String aggregateIdentifier) method.

Below some code snippet that could guide you.

data class PerformShapshotCmd(@TargetAggregateIdentifier val id: String)

    @CommandHandler
    public void handle(PerformShapshotCmd cmd, Snapshotter snapshotter) {
        logger.debug("handling {}", cmd);

        snapshotter.scheduleSnapshot(this.getClass(), cmd.getId());
    }

You should also define one Bean of type Snapshotter into your config

@Bean
public SpringAggregateSnapshotterFactoryBean snapshotter() {
    SpringAggregateSnapshotterFactoryBean springAggregateSnapshotterFactoryBean = new SpringAggregateSnapshotterFactoryBean();
    //Setting async executors
    springAggregateSnapshotterFactoryBean.setExecutor(Executors.newSingleThreadExecutor());
    return springAggregateSnapshotterFactoryBean;
}

Please note that the first argument of your commandHandler needs to be the command, otherwise the framework will complain with an exception at startup time.