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Cratis Cratis Cratis

Events

Events are immutable facts that describe what happened in your system. Chronicle identifies events by their event type rather than the .NET CLR type, which makes the CLR type a convenient vessel for expressing intent and structure.

[EventType] record
Append
Event sequence

(immutable, ordered)
Observers

(projections · reducers · reactors)
using Cratis.Chronicle.Events;


[EventType]
public record EmployeeRegistered(string FirstName, string LastName);

Event Sequences and the Event Log

Section titled “Event Sequences and the Event Log”

Events live in event sequences, which are ordered, append-only streams. Each event receives a monotonically increasing sequence number that makes it possible to replay events, resume processing, and reason about how far consumers have progressed.

Chronicle includes a specialized event sequence called the event log. It is the default sequence used throughout the system and is exposed through the IEventLog API.

using Cratis.Chronicle.Events;


public class EmployeesController(IEventLog eventLog)
{
    public Task RegisterEmployee(string firstName, string lastName) =>
        eventLog.Append(Guid.NewGuid(), new EmployeeRegistered(firstName, lastName));
}

Working with Events

Section titled “Working with Events”

Use these topics to append, read, and manage events: