If we want to fetch cities based on a selected country, which step is invalid?

The choice involving setting the Fetch property of the GetCities Aggregate to Only On Demand is not valid in this context because it limits when the data is retrieved. When fetching cities based on a selected country, the goal is to ensure that the appropriate cities are fetched when a user makes a selection in the country dropdown. Setting the Fetch property to "Only On Demand" would mean that the aggregate will only retrieve data when explicitly requested, which does not align with the immediate updating of data based on the user’s selection.

In this context, calling the GetCities Aggregate during the On After Fetch event of the GetCountries is a valid action. This approach ensures that once the countries are fetched, the application can immediately prepare to get corresponding cities based on the selected country.

Filtering the GetCities Aggregate by the selected country is also appropriate, as it directly relates the cities to the user's choice, ensuring that the correct data is displayed according to the active selection.

Additionally, refreshing the GetCities Aggregate in the OnChange Action of the Country Dropdown is a practical approach to dynamically update the displayed cities whenever a user changes the country selection. This ensures that the user always sees the most relevant data based on their current selection. Thus, the only step that does not facilitate the desired