yii报错为Array to string conversion [ 1.1 版本 ]

    $hobby[1] = "篮球";
    $hobby[2] = "足球";
    $hobby[3] = "排球";
    $hobby[4] = "台球";
    //如果用户有注册表单
    if (isset($_POST['User'])) {
        //给模型收集表单信息
        foreach ($_POST['User'] as $_k => $_v) {
            $user_model->$_k = $_v;
        }
        //实现信息存储
        if ($user_model->save()) {
            $this->redirect('./index.php?r=Index/index');//重定向到首页
        }
    }
    $this->renderPartial('register', array(
        'user_model' => $user_model,
        'sex' => $sex,
        'xueli' => $xueli,
        'hobby' => $hobby)
    );

提示这行代码有错$user_model->save()