|string> */ public function rules(): array { return [ 'topic' => 'sometimes|required|string|max:255', 'description' => 'nullable|string', 'teacher_id' => 'sometimes|required|exists:teachers,id', 'group_id' => 'sometimes|required|exists:groups,id', 'scheduled_at' => 'nullable|date', 'duration_minutes' => 'nullable|integer|min:1', ]; } }