Flex: Can I assign propertiy of multi-layer object to Chart's xField or yField?

Question

Hi, I have a question about how to assign property of a multi-layer object to Chart's xField or yField. For example:

  var obj:Object = new Object();
  var store:Object = new Object();
  store.store1 = 300;
  store.store2 = 200;
  store.store3 = 250;

  obj.date = "2010/04/26";
  obj.count = 2;
  obj.store = store;

Because I have to draw multiple LineSeries, the yField on different series must be assigned to obj.store.store1~store3. How can I set yField in different layer of object?