Filter reducers and reactors by event source type

Use [EventSourceType] on a reducer or reactor when it should only handle events appended with a specific event source type.

How the match works

Chronicle compares the observer attribute to the eventSourceType: value used when appending the event. If the values do not match, the reducer or reactor is skipped.

Filter a reactor by event source type

C#

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

[EventType]
public record FilterBySourceTypeCustomerRegistered(string EmailAddress);

public class FilterBySourceTypeCustomerRegistrationService(IEventLog eventLog)
{
    public Task Register(string emailAddress) =>
        eventLog.Append(
            EventSourceId.New(),
            new FilterBySourceTypeCustomerRegistered(emailAddress),
            eventSourceType: "customer");
}

[EventSourceType("customer")]
public class FilterBySourceTypeCustomerWelcomeReactor : IReactor
{
    public Task Registered(FilterBySourceTypeCustomerRegistered @event, EventContext context) => Task.CompletedTask;
}

The reactor is only invoked for events appended with eventSourceType: "customer".

Filter a reducer by event source type

C#

using Cratis.Chronicle.Events;
using Cratis.Chronicle.EventSequences;
using Cratis.Chronicle.Reducers;

[EventType]
public record FilterBySourceTypeInvoiceIssued(decimal Amount);

public record FilterBySourceTypeCustomerInvoiceTotal(decimal Amount);

[EventSourceType("customer")]
public class FilterBySourceTypeCustomerInvoiceTotalReducer : IReducerFor<FilterBySourceTypeCustomerInvoiceTotal>
{
    public FilterBySourceTypeCustomerInvoiceTotal Issued(FilterBySourceTypeInvoiceIssued @event, FilterBySourceTypeCustomerInvoiceTotal? current, EventContext context) =>
        new((current?.Amount ?? 0m) + @event.Amount);
}

public class FilterBySourceTypeInvoicingService(IEventLog eventLog)
{
    public Task IssueCustomerInvoice(decimal amount) =>
        eventLog.Append(
            EventSourceId.New(),
            new FilterBySourceTypeInvoiceIssued(amount),
            eventSourceType: "customer");
}

If you append the same event with eventSourceType: "supplier", this reducer does not receive it.

Combine with other filters

You can combine [EventSourceType] with [FilterEventsByTag] or [EventStreamType]. When you do, Chronicle requires all configured filter categories to match.