When you need real-time communication between Salesforce and external systems — or between components within Salesforce itself — Platform Events and Change Data Capture (CDC) are the right tools. Here's how they work and when to use each.
Platform Events vs. CDC vs. Streaming API
| Feature | Platform Events | Change Data Capture | PushTopic (legacy) | |---------|----------------|--------------------|--------------------| | Triggered by | Your Apex/Flow code | Any DML on tracked objects | SOQL query | | Custom payload | ✅ Yes | ❌ No (fixed schema) | ❌ No | | Replay supported | ✅ Yes (-1, -2, or replayId) | ✅ Yes | ❌ No | | Use case | App-to-app messaging | Sync to external systems | Deprecated |
Defining and Publishing a Platform Event
Step 1 — Create the event in Setup:
Setup → Platform Events → New Platform Event
Name: Order_Placed__e
Fields: Order_Id__c (Text), Customer_Email__c (Text), Total_Amount__c (Number)
Step 2 — Publish from Apex:
public class OrderService {
public static void publishOrderPlaced(Order__c order) {
Order_Placed__e event = new Order_Placed__e(
Order_Id__c = order.Id,
Customer_Email__c = order.Customer_Email__c,
Total_Amount__c = order.Total_Amount__c
);
Database.SaveResult result = EventBus.publish(event);
if (!result.isSuccess()) {
for (Database.Error err : result.getErrors()) {
System.debug('Error publishing event: ' + err.getMessage());
}
}
}
}Governor limit: You can publish up to 150,000 Platform Events per 24 hours on Enterprise/Unlimited editions.
Subscribing in Apex (Trigger on Event)
Create an Apex trigger on the Platform Event to handle it asynchronously:
trigger OrderPlacedTrigger on Order_Placed__e (after insert) {
List<Order_Placed__e> events = Trigger.new;
for (Order_Placed__e event : events) {
// Process each event
System.debug('Order received: ' + event.Order_Id__c
+ ' from ' + event.Customer_Email__c);
// Enqueue async work if needed
System.enqueueJob(new OrderFulfillmentQueueable(event.Order_Id__c));
}
}The trigger runs in its own transaction — failures don't affect the publisher.
Subscribing in LWC
Use the empApi wire adapter to subscribe from a Lightning Web Component:
// orderNotifications.js
import { LightningElement, wire } from 'lwc';
import { subscribe, MessageContext } from 'lightning/empApi';
export default class OrderNotifications extends LightningElement {
subscription = null;
notifications = [];
connectedCallback() {
this.subscribeToEvents();
}
subscribeToEvents() {
const channel = '/event/Order_Placed__e';
subscribe(channel, -1, (event) => {
const payload = event.data.payload;
this.notifications = [
...this.notifications,
{
id: Date.now(),
orderId: payload.Order_Id__c,
email: payload.Customer_Email__c,
amount: payload.Total_Amount__c
}
];
}).then(response => {
this.subscription = response;
});
}
}The -1 replay ID means "subscribe to new events only". Use -2 to replay all retained events (up to 72 hours).
Change Data Capture — Syncing to External Systems
CDC automatically publishes change events when records are created, updated, deleted, or undeleted. No custom code needed on the Salesforce side.
Enable CDC in Setup:
Setup → Integrations → Change Data Capture → Select objects to track (e.g., Account, Contact, Opportunity)
Subscribe from an external system (Node.js example):
const jsforce = require('jsforce');
const conn = new jsforce.Connection({
loginUrl: 'https://login.salesforce.com'
});
await conn.login(username, password);
conn.streaming.topic('/data/AccountChangeEvent').subscribe((event) => {
const header = event.payload.ChangeEventHeader;
console.log('Change type:', header.changeType); // CREATE, UPDATE, DELETE, UNDELETE
console.log('Changed fields:', header.changedFields);
console.log('Record IDs:', header.recordIds);
// Sync to your database
syncToExternalSystem(event.payload);
});Handling Replay and Errors
// Store the last processed ReplayId in a Custom Setting
public class EventReplayTracker {
public static Long getLastReplayId(String channelName) {
Event_Replay__c setting = Event_Replay__c.getInstance(channelName);
return setting != null ? (Long) setting.Replay_Id__c : -1;
}
public static void updateReplayId(String channelName, Long replayId) {
Event_Replay__c setting = Event_Replay__c.getInstance(channelName)
?? new Event_Replay__c(Name = channelName);
setting.Replay_Id__c = replayId;
upsert setting Name;
}
}Common Pitfalls
- Events are not stored permanently: Platform Events retain for 72 hours. Don't use them as a persistent log.
- Order is not guaranteed: If order matters, include a sequence number in your event payload.
- Error handling in triggers: A failed event trigger does NOT stop publishing. Build idempotent subscribers.
- CDC field-level security: CDC respects FLS for subscriber credentials. Use integration users with full field access.
