MongoDBEventSourcingRepository.java 文件源码

/**
 * Fetches the most recent version of a stream.
 * @return the most recent version.
 * @param eventStreamId
 */
public long getMostRecentStreamVersion(String eventStreamId) {
    MongoCollection<Document> casualStreams = database.getCollection(CASUAL_STREAMS_COLLECTION);
    AggregateIterable<Document> aggregate = casualStreams.aggregate(
            Lists.newArrayList(
                    new Document("$match",
                            new Document("_id", new ObjectId(eventStreamId))
                    ),
                    new Document("$group",
                            new Document("_id", "$_id")
                                    .append("maxVersion", new Document("$max", "$version_"))
                    )
            )
    );
    return Optional
            .ofNullable(aggregate.first())
            .map(d -> d.getLong("maxVersion"))
            .orElse(0L);
}