node.js - 我无法在node.js中使用mongo atlas将数据获取到另一个页面总是显示错误消息无法读取函数的属性

Question

错误

TypeError: Cannot read property 'map' of undefined
    at User.getCart (D:\udamNode\models\user.js:49:40)
    at exports.getCart (D:\udamNode\controllers\shop.js:55:6)
    at Layer.handle [as handle_request] (D:\udamNode\node_modules\express\lib\router\layer.js:95:5)
    at next (D:\udamNode\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (D:\udamNode\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (D:\udamNode\node_modules\express\lib\router\layer.js:95:5)
    at D:\udamNode\node_modules\express\lib\router\index.js:281:22
    at Function.process_params (D:\udamNode\node_modules\express\lib\router\index.js:335:12)
    at next (D:\udamNode\node_modules\express\lib\router\index.js:275:10)
    at Function.handle (D:\udamNode\node_modules\express\lib\router\index.js:174:3)

模型文件方法

getCart() {
const db = getDb();
const productIds = this.cart.items.map(i => {
  return i.productId;
});
return db.collection('products').find({ _id: { $in: productIds } }).toArray().then(products => {
    return products.map(p => {
      return {
        ...p,
        quantity: this.cart.items.find(i => {
          return i.productId.toString() === p._id.toString();
        }).quantity
      };
    });
  });

}

Controller 文件方法

exports.getCart = (req, res, next) => {req.user.getCart().then(products => {
  res.render('shop/cart', {
    path: '/cart',
    pageTitle: 'Your Cart',
    products: products
  });
}).catch(err => console.log(err));

};

Answer 1

在上面提供的代码中，this.cart.items 是未定义。这意味着当获取 user 时，结果对象在查询结果负载中不包含 cart.items。

因此，对于 mongodb，以下方法之一应该有所帮助:

1. 从数据库查询user时，必须包含items嵌套模型
2. cart 及其 items 应首先在 getCart() 方法中使用附加查询进行查询。