Observers

Reactors, reducers, and projections are all observers: something registered against an event sequence to be told about the events it cares about. eventStore.observers is how an application finds out what the event store knows about its observers, and how it removes one whose declaring code is gone.

API

eventStore.observers exposes:

• getAll() — every observer registered in the event store’s current namespace.
• remove(observerId) — removes an observer and everything keyed to it, returning an ObserverRemovalResult.

getAll() returns an ObserverInformation[]:

Property	Description
id	The identifier of the observer.
eventSequenceId	The event sequence the observer observes.
type	What kind of observer this is — Reactor, Projection, Reducer, External, or Unknown.
runningState	The state the observer is currently in.
lastHandledEventSequenceNumber	The position of the last event the observer handled.
nextEventSequenceNumber	The position of the next event the observer expects to handle.
handledEventCount	The total number of events the observer has handled.

Example

import { ChronicleClient, ChronicleOptions } from '@cratis/chronicle';

const client = new ChronicleClient(ChronicleOptions.development());
const eventStore = await client.getEventStore('MyStore');

const observers = await eventStore.observers.getAll();
for (const observer of observers) {
    console.log(`${observer.id} (${observer.type}) is ${observer.runningState}`);
}

client.dispose();

Removing an observer whose declaring code is gone

Deleting a read model and its projection, or removing a reactor, does not remove what it registered. The observer stays behind, settles into ObserverRunningState.Disconnected, and keeps its definition, state, handled counts, and failed partitions in the event store forever — until something removes them.

const result = await eventStore.observers.remove('HrNotificationReactor');
if (result.isRemoved) {
    console.log('Removed.');
} else {
    console.log(`Refused: ${result.outcome} (${result.blockingNamespace})`);
}

Removal covers the whole event store, not just the current namespace: an observer’s definition, and its projection definition where it has one, are store-level records shared by every namespace. remove refuses while the observer is running or still has a subscribed client in any namespace, and blockingNamespace names the one that blocked it, since the guard runs across all of them. There is no override — stop the declaring application first if the intent is to remove a live observer. Read model data and sink containers are left untouched; only the observer’s own bookkeeping goes.