TypeError：将循环结构转换为 JSON 节点 js

Question

当我尝试通过邮递员获取我的 api 时出现此错误

TypeError: Converting circular structure to JSON
    --> starting at object with constructor 'NativeTopology'
    |     property 's' -> object with constructor 'Object'
    |     property 'sessionPool' -> object with constructor 'ServerSessionPool'
    --- property 'topology' closes the circle

我用猫鼬和快递

const express = require('express')
const Rent = require('../model/rent')
var stringify = require('json-stringify-safe');

route = express()

route.use(express.json());

route.get('/rent', (req,res) => {
    const rents = Rent.find();
    res.send(JSON.stringify(rents))
})

module.exports = route

如果我删除 JSON.stringify 我有同样的问题 提前谢谢你

Answer 1

试试这个：

route.get('/rent', (req,res) => {          
    Rent.find({}).then((rents)=>{
        res.send(rents)
    })           
})

Answer 2

解决方案 #1

1. 在模型 Rent 上调用 find 将返回一个 Promise。
2. 我们需要 await 让 Promise 解决或在出现错误时被拒绝。
3. 始终将async\await 代码放在try-catch 块中。

const express = require('express')
const Rent = require('../model/rent')

route = express()

route.use(express.json());

route.get('/rent', async (req, res) => {
  try {
    const rents = await Rent.find().exec();
    res.send(JSON.stringify(rents));
  } catch (error) {
    res.send({error: error.message});
  }  
})

module.exports = route;

解决方案 #2：如果您想要 JSON 格式的结果。这就是我的编码方式。

* node_modules
* app.js
* db.js
* src
  - routes
    - api_router.js

文件path\to\project\app.js：

var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

const db = require("./db");

var apiRouter = require('./src/routes/api_router');

var app = express();

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/api', apiRouter);

module.exports = app;

文件path\to\project\db.js：

const mongoose = require('mongoose');
const DB_URI = "mongodb://localhost:27017/backend_app";
const DB_OPTIONS = {
  useNewUrlParser: true,
  useUnifiedTopology: true,
  useFindAndModify: false,
  useCreateIndex: true
}

(async function () {
  try {
    await mongoose.connect(DB_URI, DB_OPTIONS);
    console.log("MONGOOSE: Connected to the database!");
  } catch (error) {
    console.log("MONGOOSE ERROR");
    console.log(error);
  }
})();

文件path\to\project\src\routes\api_router.js：

const express = require('express');
const router = express.Router();

const Rent = require('../models/country_model')

router.get('/rent', async (req, res) => {
  try {
    const rents = await Rent.find().exec();
    res.status(200).json({ data: rents });           // <- Check this line.
  } catch (error) {
    res.status(500).json({ error: error.message });  // <- Check this line.
  }
})

module.exports = router;

为什么是find().exec()？

find().exec() on mongoose 函数将返回一个“真实”的 Promise 对象。 Read this.

Answer 3

Rent.find(); 可能会返回一个Promise，这就是您要在那里进行字符串化的内容。您可能会做的是await Promise 以获得所需的实际值。这应该可以解决问题：

const express = require('express')
const Rent = require('../model/rent')
var stringify = require('json-stringify-safe');

route = express()

route.use(express.json());

route.get('/rent', async (req,res) => {          // Made the controller into an `async` function to be able to use the `await` keyword
    const rents = await Rent.find();             // Await the Promise
    res.send(JSON.stringify(rents))
})

module.exports = route