JSON中的JSON eval（）数据

I am working with JSON and ajax. I am trying to post a value using AJAX. below is my issue:

My post value:

JSON:

{
    "employees": [{
        "firstName": "John",
        "lastName": "Doe"
    }]
}

I am posting JQuery eval() method it converts the JSON object as following:

&firstName=john&lastName=Deo

My problem comes when I try to post a JSON in side a JSON:

{
    "employees": [{
        "firstName": "John",
        "lastName": {
            "test1": "10",
            "test2": "12"
        }
    }]
}

When I use eval() method the above JSON object as follows:

&firstName=John&lastName=&test1=10&test2=12

My JQuery Code:

$.ajax({
        url: applicationURL,
        type: "POST",
        data: eval("(" + queryString + ")"),
        cache: false,
        dataType: "json",
        timeout: (60 * 10000),
        success: function (data) {
        },
        error: function (objAJAXRequest, strError) {
        }
    });

Is there any way to get the values of lastName as JSON object as above? Because eval() method coverts the lastName value also as & separate?

You should do something like:

$.ajax({type:"POST", data: {mydata: JSON_OBJ});

and then in PHP:

$obj = json_decode($_POST["mydata"]);

see: http://www.php.net/manual/en/function.json-decode.php