store和grid

Ext.myns.jsonds.on('load',function(store){
                            store.remove(store.getById("total"));
                            var sum;
                            sum=store.sum("Fqty");
                            //Ext.Msg.alert('sum'store.insert(store.getCount(),new Ext.data.Record({Fnumber:'合计',FitemName:'',,sum);
                            Fmodel:'',FbatchNo:'',FStockName:'',FspName:'',FunitName:'',Fqty:sum},'total'));
                        })