Define a sort method on grid for a specific column

The column values is consisted by 3 values thourg the record below:

{

text: 'ColumnA'

renderer: this.display3values,

dataIndex: 'dimensions',

flex: 3

}





display3values: function(value, metaData, record, rowIndex, colIndex, store, view) {

var str = record.get('aaa') + ' × ' + record.get('bbb') + ' × ' + record.get('ccc');

return str ;

},

But it will have problem when user want to sort it

If I want to sort the column by the product of the 3 values, how should I do ?