击倒js的多个绑定

我有多个网格，我想在一个提交按钮下运行。下面是代码:http://jsfiddle.net/aETvS/

我得到错误"Cannot read property 'push' of undefined"

    self.orders = ko.observableArray(orders);
self.addorder = function() {
    self.orders.push({
        name: "",
        price: ""
    });
};
self.removeorder = function(order) {
    self.orders.remove(order);
};

self.hardware = ko.observableArray(hardware);
self.addhardware = function() {
    self.hardware.push({
        name: "",
        price: ""
    });
};
self.removehardware = function(hardware) {
    self.hardware.remove(hardware);
};

self.save = function(form) {
    alert("Could now transmit to server: " + ko.utils.stringifyJson(self.orders));
    // To actually transmit to server as a regular form post, write this: ko.utils.postJson($("form")[0], self.orders);
};