Immutable projections as read model


This whole page will need to be revisited due to the revamped event store/projections implementation in v4. Code samples are unavailable as well.

This use case demonstrates how to create immutable projections from event streams.


To make projections immutable, the event application methods invoked by aggregators need to be made private, as well as any property setters.

-- snippet: sample_scenarios-immutableprojections-projection

To run aggregators against such projections, aggregator lookup strategy is configured to use aggregators that look for private Apply([Event Type]) methods. Furthermore, document deserialization is configured to look for private property setters, allowing hydration of the projected objects from the database.

This can be done in the store configuration as follows:

-- snippet: sample_scenarios-immutableprojections-storesetup

The serializer contract applied customizes the default behavior of the Json.NET serializer:

-- snippet: sample_scenarios-immutableprojections-serializer

Given the setup, a stream can now be projected using AggregateWithPrivateEventApply shown above. Furthermore, the created projection can be hydrated from the document store:

-- snippet: sample_scenarios-immutableprojections-projectstream