Transform functions

Use Stream.addTransform() or stream.add_transform() to map records from one Stream into another Stream. Transform functions are useful when records should be filtered, enriched, reshaped, or split before they continue through your pipeline.

Basic usage

import { Stream } from "@514labs/moose-lib"; interface RawEvent {  userId: string;  timestamp: number;} interface ProcessedEvent {  userId: string;  processedAt: Date;} const rawEvents = new Stream<RawEvent>("raw_events");const processedEvents = new Stream<ProcessedEvent>("processed_events"); rawEvents.addTransform(processedEvents, (event) => {  if (!event.userId) {    return undefined;  }   return {    userId: event.userId,    processedAt: new Date(event.timestamp),  };});

Transform behavior

• A transform reads from one source stream and writes to one destination stream.
• Return one record to emit one downstream record.
• Return undefined in TypeScript or None in Python to skip a record.
• Return an array in TypeScript or a list in Python to emit multiple downstream records from one input record.

Use a Dead letter queue when failed transforms should be captured instead of dropped.

Related capabilities

• Stream for defining the source and destination streams
• Stream.send() for getting records into the source stream
• Consumer functions when records should trigger side effects instead of writing to another stream
• Stream patterns for fan-in, fan-out, and chained stream examples
• Dead letter queues for failed-transform handling