how to update an existing json object(Apigee Baas Response) in titanium studio

hi, i am builting an android app in titanium studio with Rest api (Apigee Baas) as backend. i have some data in the Apigee Baas, for example name, address, mobile etc, now i want to update these values from my android mobile app. First in my code,i get the response from Rest API in the following manner..

{ "action" : "get",

"application" : "b97c5330-c25c-11e4-b2dd-a178ffc5bddb",

"params" : { "ql" : [ "select * where username='prii'" ] },

"path" : "/attendances",

"uri" : "https://api.usergrid.com/pri_95616/login/attendances",

"entities" : [ { "uuid" : "9d465d4a-c721-11e4-8dae-eb9b9c1ec583",

"type" : "attendance",

"created" : 1425990791444,

"modified" : 1425990791444,

"attendance" : "0",

"metadata" : { "path" : "/attendances/9d465d4a-c721-11e4-8dae-eb9b9c1ec583" }

}

now i am getting the attendance value in my code and incrementing its value and trying to update the new value to my existing to Rest API(Apigee Baas).

I have tried the following code, and in titanium studio and can any one please help me.

index.js file

function doClick(e) {

var url = "api.usergrid.com/PRI_95616/LOGIN/attendances?ql=select * where username='"+prii+"'";

var client = Ti.Network.createHTTPClient({

onload : function(e) {

var params={};

var json=JSON.parse(this.responseText);

user=json.entities[0].username;

params["username"]=user;

attn=json.entities[0].attendance;

params["attendance"]=attn;

var window = Alloy.createController('newwin', params).getView();

window.open();

}

client.open("GET", url);

client.send();

}

in the above code i am retreiving the values from the json response and want to update the value of attendance value and return it back to the same json entity.

following code i have tried to update and send back to Rest Api.

newwin.js file

var args = arguments[0] || {};

$.atn.text=args.attendance;

var abc;

abc=parseInt($.atn.text);

var url="api.usergrid.com/PRI_95616/LOGIN/attendances?";

var obj = { "username":" "+args.username+" ",

"attendance" : " "+ abc +" " };

var client = Ti.Network.createHTTPClient({

onload : function(e) { }

onerror : function(e) { }

client.setRequestHeader('content-type', 'JSON');

client.open("PUT", url);

client.send(JSON.stringify(obj));

now when i am executing this code a new entity is getting created in the Rest APi and the existing entity is not getting updated. so can any one help me on these.