EventPattern

Kind: Function

Source: packages/microservices/decorators/event-pattern.decorator.ts

Part of: Microservices

Subscribes to incoming events which fulfils chosen pattern.

EventPattern() marks a controller method as a handler for incoming microservice events that match a specified pattern. Unlike request-response message handlers, event handlers process published events without returning a response to the sender.

Signature

ts
function EventPattern(metadata: T, transportOrExtras: Transport | symbol | Record<string, any>, maybeExtras: Record<string, any>): MethodDecorator

Parameters

Returns: MethodDecorator

Diagram

mermaid
graph LR
  Publisher[Event Publisher] --> Transport[Microservice Transport]
  Transport --> Pattern{Event Pattern Match}
  Pattern -->|Matches| Handler["@EventPattern() Method"]
  Pattern -->|Does not match| Ignore[Ignore Event]
  Handler --> Process[Process Event Payload]

Usage

ts
import { Controller } from '@nestjs/common';
import { EventPattern, Payload } from '@nestjs/microservices';

@Controller()
export class OrdersEventsController {
  @EventPattern('order.created')
  handleOrderCreated(
    @Payload() order: { id: string; customerId: string },
  ): void {
    console.log(`Processing order ${order.id} for ${order.customerId}`);
  }
}

AI Coding Instructions

• Apply @EventPattern() to microservice controller methods that consume fire-and-forget events.
• Keep event patterns consistent with the names used by publishers, such as order.created or user.updated.
• Use @Payload() to receive event data and validate or transform it before performing business operations.
• Do not rely on a return value from an event handler; publishers do not receive a response for event-based communication.
• Ensure the application has a configured microservice transport capable of subscribing to the selected event pattern.

Relationships

• IMPORTS → isNil
• IMPORTS → isNumber
• IMPORTS → isObject
• IMPORTS → isSymbol

Used by

7 references from 7 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

Imported by (7)

• AppController — integration/microservices/src/app.controller.ts:20
• KafkaMessagesController — integration/microservices/src/kafka/kafka.messages.controller.ts:9
• MqttController — integration/microservices/src/mqtt/mqtt.controller.ts:16
• NatsController — integration/microservices/src/nats/nats.controller.ts:19
• RedisController — integration/microservices/src/redis/redis.controller.ts:12
• RMQController — integration/microservices/src/rmq/rmq.controller.ts:16
• AppController — integration/microservices/src/tcp-tls/app.controller.ts:22