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Your first aggregate

The Quickstart appended one event. This goes one step further into the parts that make Celeriant worth using: conditional writes and idempotency. The examples are .NET; the shape is the same in every client.

Create and append​

An aggregate is addressed by org / type / id and comes into being on its first write:

var key = new AggregateKey(orgId, ordersType, orderId);

await pool.WriteAsync(key,
    events: [new AggregateEvent
    {
        ClientSeq      = 1,
        EventTypeMajor = 1,
        EventTimestamp = DateTimeOffset.UtcNow,
        EventValue     = Encoding.UTF8.GetBytes("""{ "sku": "A-1", "qty": 2 }"""),
    }],
    allowCreate: true);

Read it back, get the version​

var details = await pool.AggregateDetailsAsync(new AggregateDetailsRequest { AggregateKey = key });
long version = details.MaxAggregateVersion;   // where the aggregate is now

Write conditionally​

The point of an event store: append only if nobody moved the aggregate since you read it. Pass the version you expect, and a stable clientId so a retry cannot double-write:

await pool.WriteAsync(key,
    events: [new AggregateEvent
    {
        ClientSeq      = 2,
        EventTypeMajor = 2,
        EventTimestamp = DateTimeOffset.UtcNow,
        EventValue     = Encoding.UTF8.GetBytes("""{ "event": "shipped" }"""),
    }],
    clientId: writerId,
    expectedVersion: version,
    enforceClientIdempotency: true);

If another writer got there first, this throws WriteOccException and nothing is appended. That is the guarantee you came for.

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