异步/等待嵌套在循环中

Question

我有一个基本的快速路由器。对数据库进行异步调用以获取数据数组。然后，使用这个数组，我正在循环执行另一个异步调用。但我不知道如何让它按照我希望它工作的顺序工作。 代码：

const db = require('../models/index');
const router = require('express').Router();
const Op = db.Sequelize.Op;

router.get('/', async function (req, res) {
  const dataSet = await db.sequelize.models.model1.findAll({
    raw: true,
    include: [{
      model: db.sequelize.models.model2,
    }, {
      model: db.sequelize.models.model3,
      required: true
    }],
    limit: 10,
    order: ['flight_date']
  });

  dataSet.forEach(async (item) => {
    delete item.id;
    const mealQtyP = await db.sequelize.models.model4.findAll({
      raw: true,
      where: {
        sampleField: sampleFieldCondition,
      }
    });

    console.log('from cycle'); //but it logged after "shall log after all"
  });

  console.log('shall log after all'); //want it to be logged after all
});

module.exports = router;

Answer 1

如果您希望在处理完dataSet 中的每个项目之后打印“毕竟应该记录”，您可以将数据集项目映射到Promises，然后再映射到await在Promise.all()。

await Promise.all(dataSet.map(async (item) => {
    delete item.id;
    const mealQtyP = await db.sequelize.models.model4.findAll({
        raw: true,
        where: {
            sampleField: sampleFieldCondition,
        }
    });

    console.log('from cycle'); //but it logged after "shall log after all"
}));

console.log('shall log after all'); //want it to be logged after all

因为你将一个异步函数传递给map，它会返回一个Promise，所以map的结果是一个Promises的数组。 Promise.all() 返回一个Promise，当数组中的所有原始Promises 都被解析时，该Promise 被解析；因此，等待这个Promise 将等到dataSet 中的每个项目都已处理完毕。

修改此代码以实际为您提供结果：

const results = await Promise.all(dataSet.map(async (item) => {
    console.log('from cycle'); //but it logged after "shall log after all"
    delete item.id;
    return db.sequelize.models.model4.findAll({
        raw: true,
        where: {
            sampleField: sampleFieldCondition,
        }
    });
}));

console.log('shall log after all'); //want it to be logged after all
console.log('here are my results:', results);