Appending with Tags

Chronicle lets you associate tags with appended events. Tags are stored as event metadata and can be used for categorization, filtering, and concurrency scoping.

Built-in metadata tags

Chronicle maintains built-in metadata tags for event identity and stream routing:

• EventSourceType
• EventSourceId
• EventStreamType
• EventStreamId

You can add custom tags in addition to these built-in tags. For the full list and behavior, see Event Metadata Tags.

Custom tags

Custom tags are simple strings that you provide when appending. They are merged with any static tags defined on the event type.

Append with tags

using Cratis.Chronicle.Events;

[EventType]
public record OrderPlaced(string CustomerId, decimal Total);

public class CheckoutService(IEventLog eventLog)
{
    public Task PlaceOrder(OrderId orderId, string customerId, decimal total)
    {
        return eventLog.Append(
            orderId,
            new OrderPlaced(customerId, total),
            tags: ["checkout", "priority"]);
    }
}

AppendMany with tags

AppendMany applies the provided tags to each event in the batch.

using Cratis.Chronicle.Events;

[EventType]
public record MoneyWithdrawn(decimal Amount);

[EventType]
public record MoneyDeposited(decimal Amount);

public class TransferService(IEventLog eventLog)
{
    public Task Transfer(AccountId fromAccount, AccountId toAccount, decimal amount)
    {
        var events = new[]
        {
            new EventForEventSourceId(fromAccount, new MoneyWithdrawn(amount)),
            new EventForEventSourceId(toAccount, new MoneyDeposited(amount))
        };

        return eventLog.AppendMany(events, tags: ["transfer", "audit"]);
    }
}