When would a developer use a custom controller instead of a controller extension?
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A. When a Visualforce page needs to replace the functionality of a standard controller. B. When a Visualforce page does not reference a single primary object. C. When a Visualforce page should not enforce permissions or field-level security. D. When a Visualforce page needs to add new actions to a standard controller.
A custom controller is an Apex class that implements all of the logic for a page without leveraging a standard controller. Use custom controllers when you want your Visualforce page to run entirely in system mode, which does not enforce the permissions and field-level security of the current user.
A controller extension is an Apex class that extends the functionality of a standard or custom controller. Use controller extensions when:
You want to leverage the built-in functionality of a standard controller but override one or more actions, such as edit, view, save, or delete.
You want to add new actions.
You want to build a Visualforce page that respects user permissions. Although a controller extension class executes in system mode, if a controller extension extends a standard controller, the logic from the standard controller does not execute in system mode. Instead, it executes in user mode, in which permissions, field-level security, and sharing rules of the current user apply.