Question

我试图更新数据库中的一堆记录，基于业余爱好网站的IMDB结果来学习Node和React。我对async / await代码和承诺相当新，所以我很难挣扎。

根据我所阅读的内容，此代码应该：

检索我所有的＆＃34; TopMovies＆＃34;来自我的数据库的记录
等待所有记录填充，然后继续
异步调用处理以更新IMDB中每条记录的一些基本字段
将每条记录保存为其异步线程的一部分
返回所有已处理的记录

相反，我得到以下控制台信息：

[0] Executing (default): SELECT `id`, `rank`, `name`, `IMDBId`, `rating`, `genre`, `posterUrl`, `createdAt`, `updatedAt`, `reviewerId`, `yearId` FROM `TopMovies` AS `TopMovie`;
[0] Movie count: 150
[0] All done
[0] Updated movie: Chef
[0] Executing (default): UPDATE `TopMovies` SET `rating`=3.5,`genre`='Adventure',`posterUrl`='https://images-na.ssl-images-amazon.com/images/M/MV5BMTY5NTYzNTA1M15BMl5BanBnXkFtZTgwODIwODU1MTE@._V1_UY268_CR0,0,182,268_AL_.jpg',`updatedAt`='2018-02-02 19:49:17.036 +00:00' WHERE `id` = 44
[0] Updated movie: The Champions
[0] Executing (default): UPDATE `TopMovies` SET `rating`=4.5,`genre`='10 October 2015 (USA) ',`posterUrl`='https://images-na.ssl-images-amazon.com/images/M/MV5BMTk5MjM2MjQ4MF5BMl5BanBnXkFtZTgwNjIxMDA5NzE@._V1_UX182_CR0,0,182,268_AL_.jpg',`updatedAt`='2018-02-02 19:49:17.092 +00:00' WHERE `id` = 87
[0] Updated movie: Trance

请注意，它在输出＆＃34;全部完成＆＃34;后更新记录，并从app.get（）函数返回。理想情况下它会更像：

[0] Executing (default): SELECT `id`, `rank`, `name`, `IMDBId`, `rating`, `genre`, `posterUrl`, `createdAt`, `updatedAt`, `reviewerId`, `yearId` FROM `TopMovies` AS `TopMovie`;
[0] Movie count: 150
[0] Updated movie: Chef
[0] Executing (default): UPDATE `TopMovies` SET `rating`=3.5,`genre`='Adventure',`posterUrl`='https://images-na.ssl-images-amazon.com/images/M/MV5BMTY5NTYzNTA1M15BMl5BanBnXkFtZTgwODIwODU1MTE@._V1_UY268_CR0,0,182,268_AL_.jpg',`updatedAt`='2018-02-02 19:49:17.036 +00:00' WHERE `id` = 44
[0] Updated movie: The Champions
[0] Executing (default): UPDATE `TopMovies` SET `rating`=4.5,`genre`='10 October 2015 (USA) ',`posterUrl`='https://images-na.ssl-images-amazon.com/images/M/MV5BMTk5MjM2MjQ4MF5BMl5BanBnXkFtZTgwNjIxMDA5NzE@._V1_UX182_CR0,0,182,268_AL_.jpg',`updatedAt`='2018-02-02 19:49:17.092 +00:00' WHERE `id` = 87
[0] Updated movie: Trance
[0] All done
* Returns from app.get

我做错了什么，这使得它说'＃34;所有完成＆＃34;在它处理任何记录之前？这是相关代码：

const imdb = require('imdb');
const _require = require('./models/index'),
  Year = _require.Year,
  Reviewer = _require.Reviewer,
  TopMovie = _require.TopMovie,
  ViewStat = _require.ViewStat,
  Op = _require.Sequelize.Op;

app.get('/imdb_import', (req, res) => {
  const UpdateMovies = async () => {
    const topMovies = await TopMovie.findAll();
    console.log("Movie count: " + _.size(topMovies));

    // await topMovies.forEach(async topMovie => {
    //   await updateMovieDetails(topMovie);
    // });
    await Promise.all(topMovies.map(async(topMovie) => {
      await updateMovieDetails(topMovie);
    }));

    console.log("All done");
    return topMovies;
  };

  const updateMovieDetails = topMovie => {
    return imdb(topMovie.get('IMDBId'), (err, data) => {
      if (err) {
        console.log(err.stack);
      }
      if (data) {
        topMovie.posterUrl = data.poster;
        topMovie.rating = Math.round(data.rating) / 2;
        if (data.genre) {
          topMovie.genre = data.genre[0];
        }
        topMovie.save();
        console.log("Updated movie: " + topMovie.name);
      }
    });
  };

  UpdateMovies()
    .then((data) => res.status(200).json(data))
    .catch(error => console.log(error));
});

此项目的代码可以在这里找到，async_imdb＆＃39;分支：https://github.com/mandreko/ov_stats/tree/async_imdb如果有人想在本地运行它

Answer 1

await updateMovieDetails(topMovie);在此代码中没有完成任何操作。请记住，await不会阻止包含函数完成并返回一个promise。它只影响函数内的代码。

因此，如果您希望使用它来对您的操作进行排序，那么它就不会这样做。此外，由于您未从.map()回调中退回任何内容，因此updateMovieDetails(topMovie)的承诺无法返回Promise.all()，因此不会等待它们。

改变这个：

await Promise.all(topMovies.map(async(topMovie) => {
  await updateMovieDetails(topMovie);
}));

到此：

await Promise.all(topMovies.map((topMovie) => {
  return updateMovieDetails(topMovie);
}));

然后，Promise.all()将等待所有updateMovieDetails()次来电完成。

此外，updateMovieDetails()不会返回与其活动相关联的承诺，因此对Promise.all()执行任何操作都无法完成任务。

您可以手动宣传imbdb()函数，然后从中返回生成的承诺：

const util = require('util');
// make promsified version of imdb()
const imdbPromise = util.promisify(imdb);

const updateMovieDetails = topMovie => {
    return imdbPromise(topMovie.get('IMDBId')).then(data => {
      if (data) {
        topMovie.posterUrl = data.poster;
        topMovie.rating = Math.round(data.rating) / 2;
        if (data.genre) {
          topMovie.genre = data.genre[0];
        }
        console.log("Updated movie: " + topMovie.name);
        topMovie.save();
      }
    });
};

以下是我推荐的积累：

const util = require('util');
// make promsified version of imdb()
const imdbPromise = util.promisify(imdb);

app.get('/imdb_import', (req, res) => {
    const UpdateMovies = async () => {
      const topMovies = await TopMovie.findAll();
      console.log("Movie count: " + _.size(topMovies));

      await Promise.all(topMovies.map(updateMovieDetails);

      console.log("All done");
      return topMovies;
    };

    const updateMovieDetails = topMovie => {
        return imdbPromise(topMovie.get('IMDBId')).then(data => {
          if (data) {
            topMovie.posterUrl = data.poster;
            topMovie.rating = Math.round(data.rating) / 2;
            if (data.genre) {
              topMovie.genre = data.genre[0];
            }
            console.log("Updated movie: " + topMovie.name);
            return topMovie.save();
          }
        });
    };

    UpdateMovies()
      .then((data) => res.status(200).json(data))
      .catch(error => console.log(error));
});

Async / Await操作超出预期顺序

1 个答案: