同步执行 Sequelize 查询

问题描述

我正在使用 Node.js 和 Sequelize(带有 Postgres 后端)构建一个网站.我有一个查询，它返回许多带有外键的对象，我想将外键引用的对象列表传递给视图.

I am building a website using Node.js and Sequelize (with a Postgres backend). I have a query that returns many objects with a foreign key, and I want to pass to the view a list of the objects that the foreign key references.

在示例中，Attendances 包含 Hackathon 密钥，我想返回一个 Hackathon 列表.既然代码是异步的，那么下面的东西在Node中当然是行不通的:

In the example, Attendances contains Hackathon keys, and I want to return a list of hackathons. Since the code is async, the following thing of course does not work in Node:

models.Attendance.findAll({
    where: {
        UserId: req.user.id
    }
}).then(function (data) {
    var hacks = [];
    for (var d in data) {
        models.Hackathon.findOne({
            where: {
                id: data[d].id
            }
        }).then(function (data1) {
            hacks.append(data1);
        });
    }
    res.render('dashboard/index.ejs', {title: 'My Hackathons', user: req.user, hacks: hacks});
});

有没有办法以同步方式进行该查询，这意味着我不会返回视图，直到我将hacks"列表填满所有对象?

Is there any way to do that query in a synchronous way, meaning that I don't return the view untill I have the "hacks" list filled with all the objects?

谢谢！

推荐答案

使用 Promise.all 执行所有查询，然后调用下一个函数.

Use Promise.all to execute all of your queries then call the next function.

models.Attendance.findAll({
    where: {
        UserId: req.user.id
    }
}).then(function (data) {
    // get an array of the data keys, (not sure if you need to do this)
    // it is unclear whether data is an object of users or an array. I assume
    // it's an object as you used a `for in` loop
    const keys = Object.keys(data)
    // map the data keys to [Promise(query), Promise(query), {...}]
    const hacks = keys.map((d) => {
      return models.Hackathon.findOne({
        where: {
          id: data[d].id
        }
      })
    })
    // user Promise.all to resolve all of the promises asynchronously
    Promise.all(hacks)
      // this will be called once all promises have resolved so
      // you can modify your data. it will be an array of the returned values
      .then((users) => {
        const [user1, user2, {...}] = users
        res.render('dashboard/index.ejs', {
          title: 'My Hackathons', 
          user: req.user, 
          hacks: users
        });
      })
});

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