如何使用诺言避免回调地狱？ [英] How to use promise to avoid callback hell?

问题描述

所以我有一个帖子集合

{
  id: String,
  comments: [String], # id of Comments
  links: [String], #id of Links
}

评论：
{
id：String，
comment：String，
}

Comments: { id: String, comment: String, }

链接：
{
id：String，
link：String，
}

Links: { id: String, link: String, }

查找包含评论和链接的帖子by id：

Find a post with comments and links belong to it by id:

Posts.findOne({id: id}, function(post) {
  Comments.find({id: post.id}, function(comments) {
    Links.find({id: post.id}, function(links) {
      res.json({post: post, comments: comment, links: links})
    })
  })
})

如何使用Promise（ http://mongoosejs.com/docs/promises.html ）以避免回调地狱？

How to use Promise(http://mongoosejs.com/docs/promises.html) to avoid callback hell?

var query = Posts.findOne({id: id});
var promise = query.exec();

promise.then(function (post) {
  var query1 = Comments.find({id: post.id});
  var promise1 = query1.exec();
  promise1.then(function(comments) {
    var query2 = Links.find({id: post.id});
    var promise2 = query2.exec();
    promise2.then(function(links) {
      res.json({post: post, comments: comment, links: links})
    })
  })
});

似乎没有好处......

Seems no good......

推荐答案

尝试使用此功能：

function getPost(id) {
  return Post
    .findOne({id: id})
    .then( post => {
      return post;
    });
}

使用 Q 模块

function getCommentsAndLinks(post) {
  return Q.all([
    Comment.find({id: post.id}),
    Links.find({id: post.id})
  ])
  .done( results => {
    let comments = results[0];
    let links = results[1];
    return [post, comments, links];
  })
  .catch( err => {
  // handle err
  })

$ b控制器上的$ b

on controller

getPost(postId)
.then(getCommentsAndLinks)
.then( results => {
  let post = results[0];
  let comments = results[1];
  let links = results[2];
  // more code here
})
.catch( err => {
// handle err
}) 

但我建议您不要保存IDS字符串，保存对象的实例，这样您就可以使用populate来获取评论和链接的所有数据，像这样：

but i suggest you not save string of IDS, save the instance of object, so you can use populate to get all data of comments and links, something like this:

Post
.findOne({id: id})
.populate('comments')
.populate('links')
.then( post => {
    // here have the post with data of comments and links
});

这篇关于如何使用诺言避免回调地狱？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！