$this->db->group_start();
$this->db->where('contracts_id_client_purchaser', $id_client);
$this->db->or_where('contracts_id_client_supplier', $id_client);
$this->db->group_end();
$this->db->where('contracts_active', 1);
$this->db->order_by('id_contracts', 'desc');
$query = $this->db->get('contracts');