ext6.0 - not able to set default index for combobox having binding define
margin: '0 0 0 0',
id:"reportsNamesId",
scope:this.controller,
forceSelection:true,
listeners: {
select: function(combo, record, index) {
console.log(mainController);
mainController.getViewModel().data.currentFilter.reportId=record.id;
}},
bind: {
store : '{reportsNames}'

},

valueField: 'abbr',
displayField: 'name',

width: 230

}

How to set default on load selection for store binding ?