Sencha Touch 2 "child store" that keeps data sync'd from a parent Ext.data.Store

ChildView.js

// A sub-store implementation that allows you to store local
// cached records in a 'parentStore', and then use this to present
// a view you can filter on for DataViews like List, etc.
//
// Dynamically selects data from parentStore, and refreshes itself
// when data in that store is changed.
//
// Allows passing a queryFunc to restrict selection of records
// from the parentStore.
Ext.define('CbMobile.store.ChildView', {
  extend: 'Ext.data.Store',
  parentStore: null,
  queryFunc: null,
  constructor: function(config) {
    config || (config == {});

    this.parentStore = config['parentStore'];
    this.queryFunc = config['queryFunc'];

    if(!this.parentStore) {
      Ext.Logger.warn('parentStore should be set in config for store.ChildView');
      return;
    }    
    
    this.callParent();
    
    // Bind & load data
    this.parentStore.on('addrecords', this.loadDataFromParent, this);
    this.parentStore.on('removerecords', this.loadDataFromParent, this);
    this.parentStore.on('updaterecord', this.loadDataFromParent, this);
    this.parentStore.on('refresh', this.loadDataFromParent, this);
    this.loadDataFromParent();
  },
  // Loads data from parent store.
  loadDataFromParent: function() {    
    var me=this;
    this.removeAll();
    
    if(this.queryFunc) {
      var results = this.parentStore.queryBy(function(record, id){
        return me.queryFunc(record, id)
      });
      this.add(results.getRange());
    } else {
      this.add(this.parentStore.getRange());
    }
  }
});

You'd use it something like...

var subStore = new CbMobile.store.ChildView({
  parentStore: Ext.getStore('SomeExistingStore')
});