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 Web Console, 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 and press Enter.
   
3. Select Notification__e Custom from the list and then press Enter.
   
4. Update the list of checkboxes so that only after insert is checked then click OK.
   

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.
   

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.