Populate store in ExtJS using hasMany associations

I am trying to populate all the records at once in a model and then assign each collective property to different container.

i.e. I have 1 grid and 1 combo on my page and trying both in one call. So I fetch the data successfully but it comes in forms of Nested JSON Data.

Ext.Model ('Person', {
  fields: [
    { name: 'firstname' },
    { name: 'lastname' },
    { name: 'placesOfWork' }
  ],
  associations: [
    { type: 'hasMany', model: 'PlaceOfWork', name: 'placesOfWork' }
});

this is my model class and whenever I try to assign it to grid so first thing I must need to iterate through each property and then create a new store at runtime to assign the data.

First I read the data by using store.reader.JsonData.placesOfWork which returns me a jsonArray and then create a store using the array elements.

Problem is not this as I got my data in grid and combo. But whenever I try to get my grid and store or comboValue then it always returns me null or store size "0"

var grid = Ext.getCmp("MyGRidID");
var store = grid.getStore();
alert(store.getCount());

It returns me 0 while data is available in my grid. similar thing happen when I try to get value from my combo which was dynamically bonded.

    var combo = Ext.getCmp("MyCombo");
    var value = combo.getValue();
    var rawValue = combo.getRawValue();

alert(value);
alert(rawValue);

Both returns null and empty value.