get primary key to put as foreign key in other table
===

I have this code, what I want to do is to get the primary key lastly inserted into the user table and then put that into the foreign key of the library table. I don't know how to do it with $request or what to do here?


    public function register($request = array()) {
        $data = array(
            'user_name' => $request['username'],
            'password' => $request['password'],
            'email' => ($request['email']) 
        );
        $data1 = array(
            'user_id' => '5',// this is where I have to put the primary key from last table
            'library_name' => $request['lib_name']
        );

        $this->model->insert('user', $data);
        $this->model->insert('library', $data1);
        $this->redirect('uploadSongs.php');
    }