Which event handler of the first aggregate can be used to refresh the query of the second aggregate?

The event handler from the first aggregate that can be used to refresh the query of the second aggregate is the 'On After Fetch' event. This event occurs after the first aggregate has completed its data fetch operation, which makes it a suitable time to trigger updates or refresh operations on other aggregates based on the data retrieved.

Using this event is effective because it ensures that the second aggregate can utilize the freshly fetched data, allowing for a more dynamic and responsive application. In scenarios where the second aggregate's data is dependent on the results of the first, refreshing it here guarantees that the second aggregate reflects any changes or updates that are coming from the processing of the first aggregate's data.

In contrast, other events, such as 'On Ready', occur when the UI component is ready to be interacted with, which may not guarantee that all necessary data has been loaded. The 'On Destroy' event is utilized for cleanup tasks when the component is being removed from the UI, while the 'After Fetch' is an ambiguous term here since it doesn’t specifically link to the event mechanisms within OutSystems’ framework. Therefore, using 'On After Fetch' is the most precise and effective choice for refreshing subsequent aggregates.