Projections API overview

This page describes the basic usage of the Projections API.

To make your stored sequence of events usable for your client, you typically define different projections/transformations. The projections are automatically maintained and updated on event.

Your projection definition consists of a number of event handlers that are applied to your events in sequence, to modify the current state of a projection. Each event handler defines processing logic for a particular event type and includes a number of options for filtering/matching event data and producing different outputs. This is how you can easily create and adapt client-specific views based on your events.

Event handlers are defined in the handlers section of your projection definition. You can add any number of handlers to your projection definition, even though it’s likely that a few will suffice for most cases.