Event store — appends and retrieves domain events. Uses a sequenced item mapper with a record manager to map domain events to database records in ways that can be easily extended and replaced.
Layer base classes — suggest how to structure an event sourced application. The library has base classes for application objects, domain entities, entity repositories, domain events of various types, mapping strategies, snapshotting strategies, cipher strategies, etc. They are well factored, relatively simple, and can be easily extended for your own purposes. If you wanted to create a domain model that is entirely stand-alone (recommended by purists for maximum longevity), you might start by replicating the library classes.
Notifications and projections — reliable propagation of application events with pull-based notifications allows the application state to be projected accurately into replicas, indexes, view models, and other applications.
Process and systems — scalable event processing with application pipelines. Parallel pipelines are synchronised with causal dependencies. Runnable with single thread, multiprocessing on a single machine, and in a cluster of machines using the actor model.
Snapshotting — avoids replaying an entire event stream to obtain the state of an entity. A snapshot strategy is included which reuses the capabilities of this library by implementing snapshots as events.
Optimistic concurrency control — can be used to ensure a distributed or horizontally scaled application doesn’t become inconsistent due to concurrent method execution. Leverages any optimistic concurrency controls in the database adapted by the record manager.
Data integrity — Sequences of events can be hash-chained, and the entire sequence of events checked for integrity. If the last hash can be independently validated, then so can the entire sequence. Events records can be encrypted with an authenticated encryption algorithm, so you cannot lose information in transit or at rest, or get database corruption without being able to detect it.
Application-level encryption — encrypts and decrypts stored events, using a cipher strategy passed as an option to the sequenced item mapper. Can be used to encrypt some events, or all events, or not applied at all (the default).
Worked examples — simple example application and systems, with an example entity class, example domain events, and an example database table. Plus lots of examples in the documentation.