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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 (App launcher icon), 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

An image showing a notification being triggered by 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.

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