How i can change value in combofield from idx to name

Form edit item

i get index of item from grid , it send to new window form

i want to change from index to name

Code:

                                        xtype : 'combo',
                    fieldLabel: 'owner',
                    name: 'prod_supplier',
                    id : 'prod_supplier',
                    allowBlank: false,
                    store: m_Supplier,
                    typeAhead:true,
                    displayField:'name',
                    valueField:'idx',
                                        listeners : {
                        'change' : function(e) {
                            e.store.setProxy({type:'ajax',url:'desktop/stock_list/supplier',reader:{root:'data'}});
                            e.store.load();    
                        }
                    }

prod_supplier is index ( number)

it want to get it and check in database then return name for me

how i can do it ?

++++++++++++++++

it will show number in field if i click to combo list it will show name from listeners