Crate eventsourced

Event sourced entities.

EventSourced is inspired to a large degree by the amazing Akka Persistence library. It provides a framework for implementing Event Sourcing and CQRS.

The EvtLog and SnapshotStore traits define a pluggable event log and a pluggable snapshot store respectively. For NATS and Postgres these are implemented in the respective crates.

The spawn function provides for creating event sourced entities, identifiable by an ID, for some event log and some snapshot store. Conversion of events and snapshot state to and from bytes happens via given Binarizer functions; for prost and serde_json these are already provided.

Calling spawn results in a cloneable EntityRef which can be used to pass commands to the spawned entity by invoking handle_cmd. Commands are handled by the command handler of the spawned entity. They can be rejected by returning an error. Valid commands produce an event with an optional tag which gets persisted to the EvtLog and then applied to the event handler of the respective entity. The event handler may decide to save a snapshot which is used to speed up future spawning.

Events can be queried from the event log by ID or by tag. These queries can be used to build read side projections.

Modules

• convert

Structs

• Binarizer
  Collection of conversion functions from and to Bytes for events and snapshots.
• EntityRef
  A handle for a spawned event sourced entity which can be used to invoke its command handler.
• NoopSnapshotStore
  A SnapshotStore implementation that does nothing.
• Snapshot
  Snapshot state along with its sequence number.

Enums

• HandleCmdError
  Error from an EntityRef.
• SpawnError
  Error from spawning an event sourced entity.

Traits

• EventSourced
  Command and event handling for an event sourced entity.
• EventSourcedExt
  Extension methods for types implementing EventSourced.
• EvtLog
  Persistence for events.
• LocalSnapshotStore
  Persistence for snapshots.
• SeqNo
  Extension methods for sequence numbers.
• SnapshotStore
  Persistence for snapshots.

Functions

• error_chain
  Format the given error with its whole error chain, implemented by using anyhow.