你如何进行“加入"?在带有 node.js 的 mongoose (mongodb) 中的数组上? [英] How do you do a "join" on an array in mongoose (mongodb) with node.js?

问题描述

如何对 mongoose 中的一系列消息进行加入"(我知道这不是正确的术语)?

How do you do a "join" (i know it is not the correct term) with an array of messages in mongoose?

我尝试遍历所有消息并查询以获取用户信息，但它不起作用:

I tried looping over all the messages and querying to get the user info but it is not working:

messages.forEach(function (message, index) {
  User.findById(message.userId, function (err, user) {
    messages[index].user = user
  })
})

console.log(messages) // the user info is not attatched

那么这是如何通过 mongoose 和 node.js 实现的?

So how is this accomplished with mongoose and node.js?

推荐答案

您的代码最大的问题是，您假设代码是同步运行的——但事实并非如此.它异步运行.所以当您执行

the biggest problem with your code is, that you assume the code to run synchronously - but it doesn't. it runs asynchronously. so messages is not yet set when you execute

 console.log(messages);

改为这样做:

var userIds = [id1, id2, id3];
User.find({"_id": {$in: userIds}}, function (err, users) {
  console.log(users);
});

编辑好的我明白了.您想将 userInfo 添加到不同的消息中.实现这一点的最简单方法是使用异步模块:https://github.com/caolan/async

edit ok, i see. you want to add the userInfo to the different messages. easiest way to acieve this, is to use the async module: https://github.com/caolan/async

async.map(messages, getUserInfo, function (err, result) {
  if (err) {
    console.log(err);
    return;
  }
  // log all msg with userinfo
  console.log(result);
});

function getUserInfo (msg, callback) {
  User.findById(msg.userId, function (err, user) {
    if (err) {
       callback(err);
       return;
    }
    msg.user = user;
    callback(null, msg);
  });
}

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