Nested grid in ExtJS 4.1 using Row Expander - extjs4.1

Question

On the front-end I have a Calls grid. Each Call may have one or more Notes associated with it, so I want to add the ability to drill down into each Calls grid row and display related Notes.
On the back-end I am using Ruby on Rails, and the Calls controller returns a Calls json recordset, with nested Notes in each row. This is done using to_json(:include => blah), in case you're wondering.
So the question is: how do I add a sub-grid (or just a div) that gets displayed when a user double-clicks or expands a row in the parent grid? How do I bind nested Notes data to it?
I found some answers out there that got me part of the way where I needed to go. Thanks to those who helped me take it from there.

Answer 1

I'll jump straight into posting code, without much explanation. Just keep in mind that my json recordset has nested Notes records. On the client it means that each Calls record has a nested notesStore, which contains the related Notes. Also, I'm only displaying one Notes column - content - for simplicity.
Ext.define('MyApp.view.calls.Grid', {
alias: 'widget.callsgrid',
extend: 'Ext.grid.Panel',
...
initComponent: function(){
var me = this;
...
var config = {
...
listeners: {
afterrender: function (grid) {
me.getView().on('expandbody',
function (rowNode, record, expandbody) {
var targetId = 'CallsGridRow-' + record.get('id');
if (Ext.getCmp(targetId + "_grid") == null) {
var notesGrid = Ext.create('Ext.grid.Panel', {
forceFit: true,
renderTo: targetId,
id: targetId + "_grid",
store: record.notesStore,
columns: [
{ text: 'Note', dataIndex: 'content', flex: 0 }
]
});
rowNode.grid = notesGrid;
notesGrid.getEl().swallowEvent(['mouseover', 'mousedown', 'click', 'dblclick', 'onRowFocus']);
notesGrid.fireEvent("bind", notesGrid, { id: record.get('id') });
}
});
}
},
...
};
Ext.apply(me, Ext.apply(me.initialConfig, config));
me.callParent(arguments);
},
plugins: [{
ptype: 'rowexpander',
pluginId: 'abc',
rowBodyTpl: [
'<div id="CallsGridRow-{id}" ></div>'
]
}]
});