Memento Persistence

A recipe for persisting Mementos (documents / snapshots) in SQL Stream Store. It's a bit like a key-value store with versions.

Why?

• The model is CRUD-Y, you don't want to use an RDMBS but want to use CQRS, streams and projections.
• The model doesn't care about domain events (or "business decisions"). The intermediate / final states are the only interesting things.
• You want to retain some or all previous versions.
• You want the option to execute a query against your memento backed object without needing a projection.

How?

• Store the memento as the message itself in a stream.
• Stream metadata decides how many previous copies to retain.
• Loading a memento is reading stream backwards by one message only so rehydrating the corresponding object is fast.

Use cases

• User settings / system configuration etc.
• Data coming from external systems where they are the source of truth.
• Snapshots for streams that are (domain) event based.

Explore

• The object that is stored and retrieved.
• ... it's memento representation
• ... the repository to load and save it.

Best thing to do is clone the repo and step through the tests.