Not Rewindable

Mark a projection as not rewindable (forward-only) using [NotRewindable]:

C#

using Cratis.Chronicle.Events;
using Cratis.Chronicle.Keys;
using Cratis.Chronicle.Projections.ModelBound;

[EventType]
public record MbNotRewindableAuditEvent(string Message, DateTimeOffset OccurredAt);

[NotRewindable]
public record MbNotRewindableAuditLog(
    [Key]
    Guid Id,

    [SetFrom<MbNotRewindableAuditEvent>(nameof(MbNotRewindableAuditEvent.Message))]
    string Message,

    [SetFrom<MbNotRewindableAuditEvent>(nameof(MbNotRewindableAuditEvent.OccurredAt))]
    DateTimeOffset Timestamp);

View C# snippet source on GitHub

Kotlin

import io.cratis.chronicle.events.EventType
import io.cratis.chronicle.projections.FromEvent
import io.cratis.chronicle.projections.NotRewindable
import io.cratis.chronicle.projections.SetFrom
import io.cratis.chronicle.readModels.ReadModel

@EventType
data class MbNotRewindableAuditEvent(val message: String, val occurredAt: String)

@ReadModel
@FromEvent(MbNotRewindableAuditEvent::class)
@NotRewindable
data class MbNotRewindableAuditLog(
    @SetFrom("message", MbNotRewindableAuditEvent::class)
    val message: String = "",

    @SetFrom("occurredAt", MbNotRewindableAuditEvent::class)
    val timestamp: String = ""
)

View Kotlin snippet source on GitHub

Java

import io.cratis.chronicle.events.EventType;
import io.cratis.chronicle.projections.FromEvent;
import io.cratis.chronicle.projections.NotRewindable;
import io.cratis.chronicle.projections.SetFrom;
import io.cratis.chronicle.readModels.ReadModel;

@EventType
record MbNotRewindableAuditEvent(String message, String occurredAt) {}

@ReadModel
@FromEvent(eventType = MbNotRewindableAuditEvent.class)
@NotRewindable
class MbNotRewindableAuditLog {
    @SetFrom(propertyPath = "message", eventType = MbNotRewindableAuditEvent.class)
    public String message = "";

    @SetFrom(propertyPath = "occurredAt", eventType = MbNotRewindableAuditEvent.class)
    public String timestamp = "";
}

View Java snippet source on GitHub

Elixir

defmodule MyApp.Events.MbNotRewindableAuditEvent do
  use Chronicle.Events.EventType, id: "mb-not-rewindable-audit-event"

  defstruct message: "", occurred_at: ""
end

defmodule MyApp.ReadModels.MbNotRewindableAuditLog do
  use Chronicle.ReadModels.ReadModel, not_rewindable: true

  defstruct id: "", message: "", timestamp: ""

  from MyApp.Events.MbNotRewindableAuditEvent,
    set: [id: :event_source_id, message: :message, timestamp: :occurred_at]
end

View Elixir snippet source on GitHub

TypeScript

import { eventType, Guid, notRewindable, setFrom } from '@cratis/chronicle';

@eventType()
export class MbNotRewindableAuditEvent {
    message = '';
    occurredAt = new Date();
}

@notRewindable
export class MbNotRewindableAuditLog {
    id: Guid = Guid.empty;

    @setFrom(MbNotRewindableAuditEvent, 'message')
    message = '';

    @setFrom(MbNotRewindableAuditEvent, 'occurredAt')
    timestamp = new Date();
}

View TypeScript snippet source on GitHub

When to use

• Audit logs or append-only data
• Projections that should never be replayed from scratch
• Time-sensitive data where replay would be incorrect

Best practices

• Use for append-only scenarios where historical replay would be problematic
• Consider carefully as this removes the ability to rebuild the projection from scratch
• Ensure you have alternative recovery strategies if the projection becomes corrupted