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Nodejs和Mongoose:Await stops循环

async-await mongoose mongodb node.js javascript

Multitut · 技术社区 · 5 年前

这是我的代码:

const csv = require('csv-parser');
const fs = require('fs');
const Customer = require('../../app/models/Customers');

const projects = [];

const processRecords = async () => {
  try {
    const usableProjects = projects.filter((project) => project['cust_number customer']);
    const customerNames = [...new Set(usableProjects.map((item) => item['Parent Name']))];
    await customerNames.forEach(async (customerName) => {
      console.log('Point 1');
      const existingCustomer = await Customer.find({Name: customerName});
      console.log('Point 2'); //<======= THIS CODE IS NEVER REACHED
      if (existingCustomer.length > 0) {
        console.log(`${customerName} already exists. Skipping...`);
        return;
      }
      const customerRecord = usableProjects.find((project) => project['Parent Name'] === customerName);
      const newCustomer = {
        Name: customerName,
        Source: 'CSV',
        Initials: customerRecord.Initials,
        Code: customerRecord.Codename,
      };
      const newCustomerRecord = await Customer.create(newCustomer);
      if (newCustomerRecord) {
        console.log(`Customer ${newCustomerRecord._id} created`);
      }
    });
  } catch (err) {
    console.log(err);
  }
};

fs.createReadStream('customer_table.csv')
  .pipe(csv())
  .on('data', async (data) => projects.push(data))
  .on('end', async () => {
    processRecords();
  });

Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1
Point 1

我知道这可能与同步/异步代码没有被我更正有关。但我没能修好。提前谢谢。

2 回复 | 直到 5 年前

marc_s HarisH Sharma 5 年前

try-catch 在一个 Customer.find() (为了清楚起见,我将简化您的代码。我会替换 客户。查找() 具有 f() )

async function success() { return "Hurrah!" }
async function failure() { throw new Error("Oops!") }

const customerNames = [1, 2, 3]

const processRecords1 = async (f) => {
    try {
        await customerNames.forEach(async (customerName) => {
            try {
                console.log('Point 1');
                const existingCustomer = await f()
                console.log('Point 2', existingCustomer);
                // ...
            } catch (err) {
                console.log('Point 3', err);
            }
        });
    } catch (err) {
        console.log('Point 4', err);
    }
};
setTimeout(() => processRecords1(success), 0);

Point 1
Point 1
Point 1
Point 2 Hurrah!
Point 2 Hurrah!
Point 2 Hurrah!

如你所见,如果 f = success 到达“点2”。所以这是第一个问题:你的 客户。查找() 失败,你看不到异常。让我们试着从为了证明这一点。。。

setTimeout(() => processRecords1(failure), 100);

输出:

Point 1
Point 1
Point 1
Point 3 Error: Oops!
Point 3 Error: Oops!
Point 3 Error: Oops!

是的,如果如果失败,我们就永远到不了“第二点”。但现在我们确实看到了一个错误,在“第3点”。所以我们可以停在这里。

processRecords() 到第四点。 forEach() 不返回值。我们试试看 map()

const processRecords2 = async (f) => {
    try {
        await customerNames.map(async (customerName) => {
            console.log('Point 1');
            const existingCustomer = await f()
            console.log('Point 2', existingCustomer);
            // ...
        });
    } catch (err) {
        console.log("Point 4", err);
    }
};
setTimeout(() => processRecords2(failure), 200);

Point 1
Point 1
Point 1
Uncaught (in promise) Error: Oops!
Uncaught (in promise) Error: Oops!
Uncaught (in promise) Error: Oops!

运气不好。是因为 地图() 确实返回一个值,但它是 Array ,不是 Promise . 你不能 await 一系列的承诺,但是你可以使用 Promise.all() https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

const processRecords3 = async (f) => {
    try {
        await Promise.all(customerNames.map(async (customerName) => {
            console.log('Point 1');
            const existingCustomer = await f()
            console.log('Point 2', existingCustomer);
            // ...
        }));
    } catch (err) {
        console.log("Point 4", err);
    }
};
setTimeout(() => processRecords3(failure), 300);

Point 1
Point 1
Point 1
Point 4 Error: Oops!
Point 4 Error: Oops!
Point 4 Error: Oops!

就这样。替换 await customerNames.forEach(...) await Promise.all(customerNames.map(...) 你可以走了。

Kevin N. 5 年前

我同意@JaromandaX,forEach不知道承诺,也不支持async/await。使用 map

Pubudu Dodangoda 5 年前

阵列 forEach map 是一条路。但是,请注意,您应该将其与 Promise.all

async function example(arr) {
  await Promise.all(
    // Assume item.fetch() returns a promise
    arr.map(item => item.fetch())
  );
}

现在,这将并行运行所有item.fetch调用。在大多数情况下,这是首选方法。但是,如果要以串行方式运行item.fetch调用,则应改用for循环。

async function example(arr) {
  for (let item of arr) {
    await item.fetch();
  }
}