NodeJS：在购物车 ID 上未定义

Question

我正在用await cartsRepo.create({ items: [] }); 定义cart 变量，但我继续在cart 上获得undefined。

我的猜测是该请求永远不会解决，因此它永远不会落入if 条件，但不确定。

部分错误是未处理的承诺拒绝，因此我将其全部放入 try/catch 块中，但我仍然在 cart 上收到 undefined。

 const express = require("express");
const cartsRepo = require("../repositories/carts");

const router = express.Router();

// Receive a post request to add an item to a cart
router.post("/cart/products", async (req, res) => {
  console.log(req.body.productId);
  // Figure out the cart!
  try {
    let cart;
    if (!req.session.cartId) {
      //   // we dont have a cart, we need to create one,
      //   // and store the cart id on the req.session.cartId property
      cart = await cartsRepo.create({ items: [] });
      req.session.cartId = cart.id;
    } else {
      //   // We have a cart! Lets get it from the repository
      cart = await cartsRepo.getOne(req.session.cartId);
    }

    const existingItem = cart.items.find(
      (item) => item.id === req.body.productId
    );
    if (existingItem) {
      // increment quantity and save cart
      existingItem.quantity++;
    } else {
      // add new product id to items array
      cart.items.push({ id: req.body.productId, quantity: 1 });
    }
    await cartsRepo.update(cart.id, {
      items: cart.items,
    });
  } catch (error) {
    console.log(error);
  }

  res.send("Product added to cart");
});

// Receive a get request to show all items in cart

// Receive a post request to delete an item from a cart

module.exports = router;

缺少的部分可能是我没有使用数据库，而是创建了这个 repository.js 文件，我的所有数据都存储在一些 json 文件中：

const fs = require("fs");
const crypto = require("crypto");

module.exports = class Repository {
  constructor(filename) {
    if (!filename) {
      throw new Error("Creating a repository requires a filename");
    }

    this.filename = filename;
    try {
      fs.accessSync(this.filename);
    } catch (error) {
      fs.writeFileSync(this.filename, "[]");
    }
  }

  async create(attrs) {
    attrs.id = this.randomId();

    const records = await this.getAll();
    records.push(attrs);
    await this.writeAll(records);
  }

  async getAll() {
    return JSON.parse(
      await fs.promises.readFile(this.filename, {
        encoding: "utf8"
      })
    );
  }

  async writeAll(records) {
    // write the updated 'records' array back to this.filename
    await fs.promises.writeFile(
      this.filename,
      JSON.stringify(records, null, 2)
    );
  }

  randomId() {
    return crypto.randomBytes(4).toString("hex");
  }

  async getOne(id) {
    const records = await this.getAll();
    return records.find(record => record.id === id);
  }

  async delete(id) {
    const records = await this.getAll();
    const filteredRecords = records.filter(record => record.id !== id);
    await this.writeAll(filteredRecords);
  }

  async update(id, attrs) {
    const records = await this.getAll();
    const record = records.find(record => record.id === id);

    if (!record) {
      throw new Error(`Record with id ${id} not found`);
    }
    // record === { email: "test@test.com" }
    // attrs === { password: 'mypassword' }
    // so attrs is copied over to record object to result in { email: "test@test.com", password: 'mypassword' }
    Object.assign(record, attrs);
    // take array of records and write it back to JSON file
    await this.writeAll(records);
  }

  async getOneBy(filters) {
    const records = await this.getAll();
    // iterate through the collection of records - for/of loop because iterating through array
    for (let record of records) {
      let found = true;
      // iterate through all key/value pairs of the filters object - for/in because iterating through object
      for (let key in filters) {
        // receive every key inside the object and can look at the value inside of object with filters[key]
        // it means email or password at filters is the same as email password on record
        if (record[key] !== filters[key]) {
          // if email and password between filters and record do not match then...
          found = false;
        }
      }
      // record was found because filters object key/value pairs and record are same
      if (found) {
        return record;
      }
    }
  }
};

Answer 1

只有一件事。如果您传递的是一个空的项目数组，那么您从无到有例外。

cart = await cartsRepo.create({ items: [] });

最后。您使用的是哪种 dB？

Answer 2

epascarello 提到，也许 cartsRepo 没有返回我所期望的结果，这让我开始考虑查看 repository.js 文件，果然问题是我忘记在 repository.js 文件中添加 return attrs;：

async create(attrs) {
    attrs.id = this.randomId();

    const records = await this.getAll();
    records.push(attrs);
    await this.writeAll(records);

    return attrs;
  }