Skip to content

Event Sequence Source

By default, model-bound projections read from the event log. Use [EventSequence] to specify a different event sequence:

C#

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

[EventType]
public record MbEventSeqOrderPlaced(decimal Amount);

[EventSequence("custom-sequence")]
public record MbEventSeqOrderSummary(
    [Key]
    Guid Id,

    [SetFrom<MbEventSeqOrderPlaced>(nameof(MbEventSeqOrderPlaced.Amount))]
    decimal TotalAmount);

This corresponds to the fluent API for declarative projections:

C#
TypeScript

using Cratis.Chronicle.EventSequences;
using Cratis.Chronicle.Projections;

[EventType]
public record MbEventSeqFluentOrderPlaced(decimal Amount);

public class MbEventSeqFluentOrderProjection : IProjectionFor<MbEventSeqFluentOrderSummary>
{
    public void Define(IProjectionBuilderFor<MbEventSeqFluentOrderSummary> builder) => builder
        .FromEventSequence(new EventSequenceId("custom-sequence"))
        .From<MbEventSeqFluentOrderPlaced>(_ => _
            .Set(m => m.TotalAmount).To(e => e.Amount));
}

public class MbEventSeqFluentOrderSummary
{
    public decimal TotalAmount { get; set; }
}

import { eventType, IProjectionBuilderFor, IProjectionFor, projection } from '@cratis/chronicle';

@eventType()
class MbEventSeqFluentOrderPlaced {
    amount = 0;
}

// The event sequence is configured on the decorator rather than the builder
@projection('', undefined, 'custom-sequence')
class MbEventSeqFluentOrderProjection implements IProjectionFor<MbEventSeqFluentOrderSummary> {
    define(builder: IProjectionBuilderFor<MbEventSeqFluentOrderSummary>): void {
        builder.from(MbEventSeqFluentOrderPlaced, _ => _
            .set(m => m.totalAmount).to(e => e.amount));
    }
}

class MbEventSeqFluentOrderSummary {
    totalAmount = 0;
}

Convenience: `[EventLog]`

Use [EventLog] when you want to be explicit that the projection reads from the default event log, even when other event types in the assembly carry a [EventStore] attribute:

C#

using Cratis.Chronicle.EventSequences;
using Cratis.Chronicle.Keys;

[EventType]
public record MbEventSeqLocalEvent(string Data);

[EventLog]
public record MbEventSeqLocalSnapshot(
    [Key]
    Guid Id,

    [SetFrom<MbEventSeqLocalEvent>(nameof(MbEventSeqLocalEvent.Data))]
    string Data);

Automatic Inbox Routing

When the event types used in a model-bound projection carry a [EventStore] attribute pointing to a different event store than the one the projection is registered in, Chronicle automatically routes the projection to the corresponding inbox sequence — no [EventSequence] annotation needed.

When the [EventStore] attribute points to the same event store as the current one, Chronicle routes to the event log instead.

When to use `[EventSequence]` explicitly

When you need to read from a specific sequence other than the inferred one
To suppress automatic inbox routing for a projection that handles foreign events
For projections that target a specialized or partitioned event stream

Note: The old [FromEventSequence] attribute has been removed. Use [EventSequence] instead.