Option B is correct because platform events are published after the Apex transaction completes. Platform events are asynchronous messages that are published and consumed by different processes or systems. When an Apex transaction publishes a platform event, the event is not sent immediately, but rather added to a temporary queue. The event is only published and delivered to the subscribers after the Apex transaction commits successfully. This ensures that the event data is consistent with the database state and that the event is not lost in case of a rollback.
Option A is incorrect because platform events are not published immediately before the Apex transaction completes. As explained above, platform events are published after the Apex transaction commits successfully. Publishing events before the transaction completes can cause data inconsistency and event loss issues.
Option C is incorrect because platform events can have a trigger in Apex, but this is not related to the question of when events are published. A platform event trigger is a special type of Apex trigger that executes when a platform event message is received by Salesforce. A platform event trigger can perform logic based on the event data, such as updating records, sending notifications, or calling external services. A platform event trigger does not affect the publishing of events, but rather the consumption of events.
Option D is incorrect because platform events can be published from Apex, but this does not answer the question of when events are published. Platform events can be published from various sources, such as Apex code, Process Builder, Flows, or API calls. Publishing events from Apex requires creating an instance of a platform event object and using the EventBus.publish method to add it to the temporary queue. The actual publishing of events happens after the Apex transaction completes, regardless of the source of the events.
[References: Publish and Subscribe with Platform Events: Publish Platform Events : Subscribe to Platform Events : Write a Platform Event Trigger : Create and Publish Platform Events in Apex : EventBus Class, , , ]
