Publish a Platform Event

In this last step, you implement a Chatter Apex trigger that triggers a notification for each post containing the #BearAlert topic.

Implement a Chatter Apex Trigger

1. Create an Apex trigger named BearAlertTopicAssignmentTrigger:
   1. In Visual Studio Code, under force-app/main/default, right-click the triggers folder and select SFDX: Create Apex Trigger.
   2. Enter BearAlertTopicAssignmentTrigger for the name of the trigger.
   3. Press Enter and then press Enter again to accept the default force-app/main/default/triggers.
2. Replace the default code with this:

   trigger BearAlertTopicAssignmentTrigger on TopicAssignment (after insert) {
       // Get FeedItem posts only
       Set<Id> feedIds = new Set<Id>();
       for (TopicAssignment ta : Trigger.new){
           if (ta.EntityId.getSObjectType().getDescribe().getName().equals('FeedItem')) {
               feedIds.add(ta.EntityId);
           }
       }
       // Load FeedItem bodies
       Map<Id,FeedItem> feedItems = new Map<Id,FeedItem>([SELECT Body FROM FeedItem WHERE Id IN :feedIds]);
       // Create messages for each FeedItem that contains the BearAlert topic
       List<String> messages = new List<String>();
       for (TopicAssignment ta : [SELECT Id, EntityId, Topic.Name FROM TopicAssignment WHERE Id IN :Trigger.new AND Topic.Name = 'BearAlert']) {
           messages.add(feedItems.get(ta.EntityId).body.stripHtmlTags().abbreviate(255));
       }
       // Publish messages as notifications
       List<Notification__e> notifications = new List<Notification__e>();
       for (String message: messages) {
           notifications.add(new Notification__e(Message__c = message));
       }
       List<Database.SaveResult> results = EventBus.publish(notifications);
       // Inspect publishing results
       for (Database.SaveResult result : results) {
           if (!result.isSuccess()) {
               for (Database.Error error : result.getErrors()) {
                   System.debug('Error returned: ' + error.getStatusCode() +' - '+ error.getMessage());
               }
           }
       }
   }

   Code Highlights:
   • The trigger intercepts all new Chatter posts that contain one or more topics.
   • If a post contains the #BearAlert topic, the trigger publishes the post message as a notification through the standard EventBus utility class. Errors are checked after publication.
3. Save the file.
4. Right click on the triggers folder and select SFDX: Deploy Source to Org to deploy your trigger to your org.

Test the Chatter Trigger

Now you can test your work. Create a Chatter post to ensure that it triggers a notification.

1. From the App Launcher (), find and select Sales, or if the Sales app is already open, refresh the browser.
2. Click Chatter.
3. Create a new post with the following content:

   #BearAlert False alarm: It's just a big dog!

At this point, your message appears both as:

• A notification toast
• A Chatter post

Project Summary

Congratulations, you are now a platform events expert!

Now you know how to define a platform event, how to publish events with Apex, and how to subscribe to events via a Lightning component that uses the lightning/empApi module.

You can apply your newly gained knowledge to build your own event-driven applications.