Ext.EditGrid ColumnModel renderer 问题

{ header: "产品名称", width: 160, dataIndex: 'product_id',
                        renderer: function(value, cellmeta, record) {
                            var index = productInfoStore.find(productCmb.valueField, value);
                            var record = productInfoStore.getAt(index);
                            var displayText = "";
                            if (record == null) {
                                displayText = value;                            } else {
                                displayText = record.data.Name;
                            }
                            return displayText;
                        },
                        editor: productCmb
                    },
{ header: "价格", width: 60, dataIndex: 'order_amt', editor: new Ext.form.TextField(),
                        renderer: function(value, cellmeta, record) {
                            var prd_count = record.get('prd_count');
                            var product_id = record.get('product_id');
                            var ore = productCmb.getStore().getById(product_id);
                            if (ore) {
                               return ore.get('UnitPrice') * prd_count;
                            } else {
                              return value;
                            }
                        }
                    } var m = productStore.getModifiedRecords();
      if (m.length > 0) {
           for (var i = 0, len = m.length; i < len; i++) {
                 alert(m[i].data["prod_batch"] + ":" + m[i].data["order_amt"]);
          }
                                  
    }
为什么alert售价是undefined，