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Stream filtering

Layer 0: CloudEvents

org.occurrent.eventstore.api.StreamReadFilter is an EventStore read capability for cases where a command or use case only depends on a subset of the events in a stream. It is useful when you want to avoid reading and deserializing events that are irrelevant for a specific decision.

Filtering is a read optimization, not a correctness feature. Do not filter away events that are needed to enforce invariants, rebuild state correctly, or make valid domain decisions.

StreamReadFilter is intentionally scoped to stream reads and validates reserved stream fields such as streamid and streamversion.

Filtered stream reads are exposed via optional capability interfaces:

  • org.occurrent.eventstore.api.blocking.ReadEventStreamWithFilter
  • org.occurrent.eventstore.api.reactor.ReadEventStreamWithFilter

The following event stores support filtered stream reads:

  • InMemoryEventStore
  • MongoEventStore
  • SpringMongoEventStore
  • ReactorMongoEventStore

A blocking example:

if (eventStore instanceof ReadEventStreamWithFilter filteredEventStore) {
    EventStream<CloudEvent> eventStream = filteredEventStore.read(
            "streamId",
            StreamReadFilter.type("com.acme.NameDefined")
    );
}

A reactor example:

if (eventStore instanceof org.occurrent.eventstore.api.reactor.ReadEventStreamWithFilter filteredEventStore) {
    Mono<EventStream<CloudEvent>> eventStream = filteredEventStore.read(
            "streamId",
            StreamReadFilter.type("com.acme.NameDefined")
    );
}