异常:查询结果集不可修改

我正在尝试使用以下代码写入JDO存储:

    PersistenceManager pm = PMF.get().getPersistenceManager();

    try {
        pm.currentTransaction().begin();

        // deactivate all for current domain
        Query q = pm.newQuery(CampaignStore.class, "domain == '" + domain +"'");
        Collection result = (Collection) q.execute();

        CampaignStore toBeEdited = null;
        Iterator iter = result.iterator();
        while (iter.hasNext()) {
            toBeEdited = (CampaignStore) iter.next();
            toBeEdited.setActive(false);
        }
        result.clear();

        // set new one active
        q = pm.newQuery(CampaignStore.class, "id == " + id);
        result = (Collection) q.execute();
        toBeEdited = (CampaignStore) result.iterator().next();
        if (toBeEdited == null) {
            LOG.log(Level.WARNING, "setActiveCampaign: Unable to find Campaign ID '"+ id +"'");
            pm.currentTransaction().rollback();
            return;
        }           
        toBeEdited.setActive(true);

        pm.currentTransaction().commit();
        LOG.log(Level.INFO, "setActiveCampaign: Active Campaign ID is now '"+ id +"'");
    }
    catch (Exception e) {
        pm.currentTransaction().rollback();
        LOG.log(Level.WARNING, "setActiveCampaign: Exception: "+ e.getMessage());
    } finally {
        pm.close();
    }

不幸的是,我得到一个“查询结果集不可修改”异常。

我非常肯定它来自于第一个带有迭代的查询,因为第二个查询本身就可以工作。

我需要更改什么才能修改查询结果?