Live Aggregations

Live aggregation replays events on demand to build the current aggregate state without persisting a read model.

Basic Usage

var order = await session.Events.AggregateStreamAsync<OrderSummary>(streamId);

This loads all events for the stream and applies them through the aggregate's Create and Apply methods.

When to Use Live Aggregation

Live aggregation is best for:

• Infrequently accessed aggregates -- No need to maintain a persistent read model
• Always-current state -- No staleness, always reflects the latest events
• Streams with few events -- Low replay cost
• Testing and debugging -- Verify aggregate behavior

Version Cap

Replay only up to a specific version:

var orderAtV5 = await session.Events.AggregateStreamAsync<OrderSummary>(streamId, version: 5);

Timestamp Cap

Replay only events before a specific time:

var orderAtTime = await session.Events.AggregateStreamAsync<OrderSummary>(
    streamId,
    timestamp: DateTimeOffset.Parse("2024-06-15")
);

With Snapshots

If a snapshot exists for the stream, AggregateStreamAsync automatically uses it to optimize replay:

1. Load the snapshot from pc_streams
2. Only replay events after the snapshot version
3. Return the hydrated aggregate

See Snapshots for details on configuring snapshot storage.

Live vs Inline vs Async

Strategy	Consistency	Storage	Performance
Live	Always current	None	Replay cost per read
Inline	Always current	Document table	Write overhead
Async	Eventually consistent	Document table	Background processing