The core domain functions
1decide
let decide cmd state : EventAction<Event>Validate, decide, and emit events.
2fold
let fold event state : StateEvolve state from events.
Event-sourced CQRS for .NET
Focus on your business rules. FCQRS handles the rest.
The rest: event storage, recovery, projections, sagas, and correlation-based read-your-writes.
Start with two pure domain functions, then learn where storage, recovery, and distributed boundaries matter.
First-class support for C# and F#
dotnet add package FCQRSthen follow the learning pathHow a request becomes a query result
Command
A request to change one aggregate.
decide
Choose an event from the command and current state.
Events
Immutable facts appended to the journal.
2fold
Applies events to aggregate state, live and during replay.
Projections
Update read models asynchronously: the views your application queries.
Runtime responsibilities
Durable journal
Persisted events rebuild aggregate state after restart.
Sagas
Stored workflow state coordinates commands across aggregates.
Recovery
Aggregates and sagas replay stored history before processing.
Read-your-writes
Wait for a selected projection before querying its view.
Snapshots
Capture state for faster replay and recovery.
Also built in Telemetry & health signals Structured logging
Why this matters
Reliable by default
- Commands are serialized per aggregate
- Stored events are replayable history
- Saga progress survives process restart
- Projection completion can be awaited
- Snapshots shorten aggregate replay
Ready when you grow
- Read models are shaped per query
- Cluster sharding routes aggregate ids
- Built on Akka.NET
- Aggregates can run across cluster nodes
- Storage and projections remain explicit choices
Focus on your domain
- Business decisions live in
decide - Recovery logic lives in
fold - Testable without a runtime
- Commands and events document outcomes
- Infrastructure boundaries stay visible