将数据库中的ID传递给URL - CodeIgniter

I am starting my game with CodeIgniter and I have a problem - I would like to download the ID - of the product from the database so that it will be passed to the URL address:

Example address:

http://localhost/crm-SEO/api/admin/domains/{{ID in database}}/notes

When I have other methods like:

domains/GET/6
domains/update/6

Everything works fine for me, but I can not grasp it that I have domains/{{ID}}/

My code i models:

public function get( $id = false)
    {
        if ( $id == false ) {
            $q = $this->db->get('domains');
            $q = $q->result();
        }
        else{
            $this->db->where('id', $id);
            $q = $this->db->get('domains');
            $q = $q->row();
        }
        return $q;
    }

    public function update($domain)
    {
        $this->db->where('id', $domain['id'] );
        $this->db->update('domains', $domain);
    }

    public function create($domain)
    {
        $this->db->insert('domains', $domain);
    }

    public function delete($domain)
    {
        $this->db->where('id', $domain['id'] );
        $this->db->delete('domains');
    }

My code in controller:

public function __construct()
    {
        parent::__construct();

        $post = file_get_contents('php://input');
        $_POST = json_decode($post,true);
        $this->load->model('admin/domains_model');
    }

    public function get($id = false)
    {
        $result = $this->domains_model->get($id);
        echo '{"records":' . json_encode( $result ) . '}';
    }

    public function update()
    {
        $domain = $this->input->post('domain');
        $this->domains_model->update($domain);
    }

    public function create()
    {
        $domain = $this->input->post('domain');
        $this->domains_model->create($domain);
    }

    public function delete()
    {
        $domain = $this->input->post('domain');
        $this->domains_model->delete($domain);
    }