I'm trying to display multi-series chart with dynamic number of series.
From data servicing perspective the best would be if I able to have model similar to this -
Ext.define('MyApp.model.Statistics', {
    extend: 'Ext.data.Model',
    fields: [
        {  name: 'date', dataType: 'date'     },
        {  name: 'category',  dataType: 'int' },
        {  name: 'data',    dataType: 'number'   }
and so the the store after getting data from web API will look something like -

Data: [ 
{ date:"1/1/2013", cat:"1", data:"0.23" },
{ date:"1/1/2013", cat:"2", data:"0.32" },
{ date:"1/1/2013", cat:"3", data:"0.23" },
{ date:"1/2/2013", cat:"1", data:"0.56" },
{ date:"1/2/2013", cat:"2", data:"0.57" },
{ date:"1/2/2013", cat:"3", data:"0.22" },
.....and so on
in above case number of categories is 3 and is known number before I'm going to build a chart.
All I need is 3-series-chart reflecting this data.

I understand that in default implementation chart needs pivoted structure like
{ date:"1/1/2013", cat1_data:"0.23",cat2_data:"0.32",cat3_data:"0.23"  },
{ date:"1/2/2013", cat1_data:"0.56",cat2_data:"0.57",cat3_data:"0.22"  },
.....and so on
which both - limiting chart functionality and making server-side process heavier.
In other words I consider it as a worst solution.

I'm sure you people have done it. Please give me some direction. Any thoughts are greatly appreciated!