Write Events

The writeEvents function persists one or more Nimbus events to EventSourcingDB. It automatically converts Nimbus events to EventSourcingDB event candidates, injects OpenTelemetry trace context, and supports preconditions for optimistic concurrency control.

An in Depth Example

This guide also has an in depth example of a working application built with EventFabric. Combining DDD, CQRS and Event Sourcing.

Check out the In Depth Example page to learn how everything is connected and works out in a real-world application.

Basic Usage

import { createEvent } from "@eventfabric-cqrs/core";
import { writeEvents } from "@nimbus-cqrs/eventsourcingdb";
import { isSubjectPristine } from "eventsourcingdb";

const event = createEvent({
    type: "at.overlap.nimbus.user-invited",
    source: "nimbus.overlap.at",
    correlationid: command.correlationid,
    subject: `/users/${id}`,
    data: {
        email: "john@example.com",
        firstName: "John",
        lastName: "Doe",
        invitedAt: new Date().toISOString(),
    },
});

await writeEvents([event], [isSubjectPristine(event.subject)]);

Function Parameters

Parameter	Type	Description
events	Event[]	An array of Nimbus events to write
preconditions	Precondition[]	Optional preconditions that must be met for the write to succeed

Preconditions

EventSourcingDB supports the following preconditions. For full details, see the Using Preconditions section in the EventSourcingDB documentation.

To use these preconditions, you can directly import them from the EventSourcingDB JavaScript SDK.

OpenTelemetry Tracing

Every call to writeEvents is automatically wrapped in an OpenTelemetry span named eventsourcingdb.writeEvents. The current trace context (traceparent and tracestate) is injected into each event candidate, enabling end-to-end distributed tracing from the event writer to any event observer that processes the event.

The following metrics are recorded:

Metric	Type	Labels	Description
eventsourcingdb_operation_total	Counter	operation, status	Total number of write operations
eventsourcingdb_operation_duration_seconds	Histogram	operation	Duration of write operations in seconds