cara edit data sesuai sesi yg aktif

saya punya coding kayak begini tapi malah error karena id-nya primary key.. solusi?

function m_edit_profil(){
  $edit_profil = array(
    'id' => $this->session->userdata('id'),
    'nama' => $this->input->post('nama'),
    'nama_kepsek' => $this->input->post('nama_kepsek'),
    'nip_kepsek' => $this->input->post('nip_kepsek'),
    'daerah' => $this->input->post('daerah'),
    'password' => md5($this->input->post('password'))
    );
  $edit = $this->db->update('user', $edit_profil);
  return $edit;
}