private function findPreviousUpdate($assignmentId) { $previousAssignmentIdCached = Cache::get('previous_assignment_id_for_' . $assignmentId); if ($previousAssignmentIdCached !== null) { return $previousAssignmentIdCached; } else { $ascUpdates = AssignmentUpdate::where('assignment_id', $assignmentId)->orderBy('created_at', 'DESC')->get()->last(); return $ascUpdates; } }