mongodb nodejs - 转换循环结构

问题描述

我有一些代码可以从集合中提取所有文档并将其放到网页上。简化版本如下所示：

I have some code that pulls all documents from a collection and puts it onto a webpage. a simplified version looks like this:

var mongodb = require("mongodb"),
    express = require("express"),
    mongoServer = new mongodb.Server('localhost', 27017),
    dbConnector = new mongodb.Db('systemMonitor', mongoServer),
    db;

var app = new express();

app.get('/drives', function(req, res) {
  db.collection('driveInfo', function(err, collection) {
    if (err) throw err;
    collection.find({}, function(err, documents) {
      res.send(documents);
    });
  });
});

dbConnector.open(function(err, opendb) {
  if (err) throw err;
  db = opendb;
  app.listen(80);
});

我有一个包含很长文档列表的driveInfo集合。每个文档都包含嵌套对象。我想做的是，每当有人在他们的浏览器中访问/驱动时，将整个集合打印为json对象，以便我可以稍后使用jquery抓取所有内容（api的开头）

I have a driveInfo collection which contains a long list of documents. Each document contains nested objects. What I would like to do, is whenever someone visits /drives in their browser, to print the entire collection as a json object so that I can grab everything with jquery later (beginnings of an api)

但是，我收到错误提示TypeError：将循环结构转换为JSON。页面上的错误指向这行代码：

However, I get an error saying "TypeError: Converting circular structure to JSON". The error on the page points to this line of code:

collection.find({}, function(err, documents) {
  res.send(documents);
});

我不确定问题是什么，或者自我引用的位置。我没有正确查询集合吗？

I'm unsure what the problem is, or where the self-reference is. Am I not querying the collection properly?

推荐答案

不确定您使用的是哪个版本的API，但我认为您的语法查看API规范可能有误：

Not sure what version of the API you are using, but i think that your syntax might be wrong looking at the API spec:

这是声明：

db.collection.find(<criteria>, <projection>)

你肯定在滥用投影参数。像你一样传递回调似乎返回结果中的 db 对象，这导致在快递中JSON序列化期间出现循环错误。

And you are definitely misusing the projection parameter. Passing a callback like you are doing seems to return the db object in the result, which is causing the circular error during JSON serialization in express.

查找所有操作的正确代码应该类似于：

The correct code for the find all operation should be something like:

collection.find({}).toArray(function(error, documents) {
    if (err) throw error;

    res.send(documents);
});

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