访问ajax数据对象属性

Question

如果我有ajax生成的数据对象，我如何访问TotalCashBack值？ 我试过var $ total_amt = data.TotalCashBack;但它返回undefined

    Object]0: Object
TotalCashBack: "9.00"
__proto__: Object..... function __proto__() { [native code] }length: 1__proto__: Array[0] 

这是我的ajax代码：

function getCashBackTotalAmount(u_email){

    console.log('cashback value');

    $.ajax({
        url: 'userprofile/gettotalcashback',
        data : {email:u_email},
        dataType: 'json',
        success: function(data){
            console.log('success getTotalCashBack');
            console.log(data);

            var $total_amt = data.TotalCashBack;
            console.log($total_amt);
            $('.earning > span').replaceWith($total_amt);
            console.log(data.length);

        },error : function(){
            console.log("error getTotalCashBack");
        }

        });
}

我实际上使用的是MVC。 这是我的建模者：

 function gettotalcashback($email, $mediaid){       

       $db_user = $this->load->database('cashback_user',TRUE);
       $q = "SELECT SUM(cb_amnt) as TotalCashBack from cashback_sale WHERE email='".$email."' AND media_id=".$mediaid;

       $q_usr = $db_user->query($q);

        if ($q_usr->num_rows() > 0)
        {

           return ($q_usr->result());



        }



    }

这是我的控制器：

public function gettotalcashback(){
    global $data, $f;

    $media = get_cookie('cb_media');

    $f = false;
    $total_cashback = $this->pfm->gettotalcashback($_GET['email'], $media);

    echo json_encode($total_cashback);

}