XML-RPC通过外部id读取

我有一个场景在这里，我需要读取/检索元素从openerp/odoo使用xml-rpc外部id。我使用的技术是php。下面是我从odoo读取/检索数据的代码函数:

public function read($ids, $fields, $model_name, $context=array() ) {
    $client = new xmlrpc_client($this->server."object");
    //  ['execute','userid','password','module.name',{values....}]
    $client->return_type = 'phpvals';
    $id_val = array();
    $count = 0;
    foreach ($ids as $id)
        $id_val[$count++] = new xmlrpcval($id, "int");
    $fields_val = array();
    $count = 0;
    foreach ($fields as $field)
        $fields_val[$count++] = new xmlrpcval($field, "string");
    $msg = new xmlrpcmsg('execute');
    $msg->addParam(new xmlrpcval($this->database, "string"));  //* database name */
    $msg->addParam(new xmlrpcval($this->uid, "int")); /* useid */
    $msg->addParam(new xmlrpcval($this->password, "string"));/** password */
    $msg->addParam(new xmlrpcval($model_name, "string"));/** model name where operation will be held * */
    $msg->addParam(new xmlrpcval("read", "string"));/** method which u like to execute */
    $msg->addParam(new xmlrpcval($id_val, "array"));/** ids of record which to be updated...This array must be xmlrpcval array */
    $msg->addParam(new xmlrpcval($fields_val, "array"));/** parameters of the methods with values....*/
    //values added
    $ctx = array();
    foreach($context as $k=>$v){
       $ctx[$k] = new xmlrpcval( xmlrpc_get_type($v) );
    }
   //end
    if(!empty($context)){
       // $msg->addParam(new xmlrpcval(array("lang" => new xmlrpcval("nl_NL", "string"),'pricelist'=>new xmlrpcval($context['pricelist'], xmlrpc_get_type($context['pricelist']) )) , "struct"));
    }
    $resp = $client->send($msg);
    print_r($resp);
    if ($resp->faultCode())
        return -1;   /* if the record is not writable or not existing the ids or not having permissions*/
    else
        return $resp->value();
}

它只给出了id和名称在我这边没有给我odoo中数据的特定外部id我试图从odoo中读取