node.js - 在 forEach 循环中运行 sequelize 查询。无法处理结果

Question

我正在运行这个 sequelize 查询，它返回一些论坛帖子。对于每个结果，我运行第二个查询，它为我提供每个论坛帖子的类别/标签。现在，forEach 循环在所有查询运行之前结束，因为它是异步的，我知道那部分。我如何正确处理这个问题并做我想做的事情？我想将标签/类别数组附加到每个帖子并将帖子数组发送到 ejs View 并调用 next();

我已经尝试过 promise.all() 和 async-await，我确实以这种方式分别获得了类别。但我希望将类别附加到每个帖子对象。

Forum.findAll({
    attributes: ["f_post_id", "f_post_title", "like_count", "createdAt"],
    limit: limitPost.FORUM,
    subQuery: false,
    raw: true,
    group: ['forum.f_post_title'],

    include: [{
        attributes: ["user_name"],
        model: User,
        required: true, // returns everything in a clean single object format
                        // setting it to false, results in nested arrays
    }, {
        attributes: [[Sequelize.fn("COUNT", Sequelize.col("forum_answers.answer_id")), "ansCount"]],
        model: ForumAnswer,
        required: true,
    }]
})
    .then(fetchedPost => {

        fetchedPost.forEach(post => {

            ForumTag.findAll({
                attributes: [],
                raw: true,

                where: {
                    f_post_id: post.f_post_id,
                },
                include: [{
                    attributes: ["tag_name"],
                    model: Tag,
                    required: true,
                }]
            })
                .then(postTags => {

                    post.tags = postTags.map(postTag => postTag["tag.tag_name"]);

                })
                .catch(err => console.log(err));

        });

        res.locals.fetchedPost = fetchedPost;
        next();

    })
    .catch(err => console.log(err));

这是下面的预期结果:

{ 
  f_post_id: 1,
  f_post_title: 'learn js',
  like_count: 12,
  createdAt: 2019-05-19T00:00:00.000Z,
  'user.user_name': 'mrscx',
  'forum_answers.ansCount': 3,
  tags: [ 'JavaScript', 'Database' ] 
}

但是由于 forEach 循环结束，标签没有被附加。

我该如何解决？

Answer 1

从表面上看，问题可能与您处理 promise 的方式有关。您实际上并不是在等待 forEach 循环中的 promise 被处理，而是在此之前返回结果。解决这个问题的一种方法是:

Forum.findAll({
    attributes: ["f_post_id", "f_post_title", "like_count", "createdAt"],
    limit: limitPost.FORUM,
    subQuery: false,
    raw: true,
    group: ['forum.f_post_title'],

    include: [{
        attributes: ["user_name"],
        model: User,
        required: true, // returns everything in a clean single object format
                        // setting it to false, results in nested arrays
    }, {
        attributes: [[Sequelize.fn("COUNT", Sequelize.col("forum_answers.answer_id")), "ansCount"]],
        model: ForumAnswer,
        required: true,
    }]
})
    .then(fetchedPost => {

        return Promise.all(fetchedPost.map(post => 
            ForumTag.findAll({
                attributes: [],
                raw: true,

                where: {
                    f_post_id: post.f_post_id,
                },
                include: [{
                    attributes: ["tag_name"],
                    model: Tag,
                    required: true,
                }]
            })
                .then(postTags => {

                    post.tags = postTags.map(postTag => postTag["tag.tag_name"]);
                    return post.save();
                })
                .catch(err => console.log(err));

        }).then(() => {
          res.locals.fetchedPost = fetchedPost;
          next();
      });
    })

我敢肯定，还有更优雅的方法可以做这种事情。但这是对原始代码的最少修改。