A controller extension is an Apex class that extends the functionality of a standard or custom controller.
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.