Subscribe Reactors to External Event Stores

Automatic Inbox Routing

When all event types handled by a reactor come from the same source event store, Chronicle routes the reactor to the matching inbox sequence automatically:

Source event store: fulfillment-service
Inbox sequence observed by the reactor: inbox-fulfillment-service

This works when the source is declared on event types (or assembly) using [EventStore("...")], and no explicit event sequence is configured on the reactor.

using Cratis.Chronicle.Events;
using Cratis.Chronicle.Reactors;

[EventType]
[EventStore("fulfillment-service")]
public record ShipmentDispatched(Guid OrderId, string TrackingNumber);

public class FulfillmentReactor : IReactor
{
    public Task ShipmentDispatched(ShipmentDispatched @event, EventContext context) => Task.CompletedTask;
}

Observer-Level EventStore for Missing Event Metadata

When event contracts cannot carry [EventStore] metadata, apply [EventStore] directly on the reactor.

Chronicle resolves the reactor to the inbox for that source event store and implicitly creates or reuses the outbox-to-inbox subscription.

using Cratis.Chronicle.Events;
using Cratis.Chronicle.Reactors;

[EventType]
public record ExternalUserInvited(Guid UserId);

[EventStore("identity-service")]
[Reactor]
public class ExternalUserInvitedReactor : IReactor
{
    public Task On(ExternalUserInvited @event, EventContext context) => Task.CompletedTask;
}

Implicit Combined Event Type Filtering

For each source event store, Chronicle combines all reactor and reducer event types into one implicit subscription filter.

This means:

You get one subscription per source event store.
The filter is the union of handled event types from all participating observers.
Only those event types are forwarded from source outbox to target inbox.

Explicit Event Sequence Is Not Allowed with Observer EventStore

When a reactor has [EventStore("...")], do not combine it with:

[EventSequence("...")]
[EventLog]
[Reactor(eventSequence: "...")]

This is invalid and fails:

At runtime with EventStoreCannotBeCombinedWithExplicitEventSequence.
At compile time with analyzer rule CHR0013.

Subscribe Reactors to External Event Stores

Automatic Inbox Routing

Observer-Level EventStore for Missing Event Metadata

Implicit Combined Event Type Filtering

Explicit Event Sequence Is Not Allowed with Observer EventStore

See Also