Question

我是node.js的新手

我只是制作一个简单的应用程序我的数据正确插入数据库以及从数据库中取出但问题是，当我试图在json模型中访问它时，它给了我错误

var express = require('express');

/*
 * body-parser is a piece of express middleware that 
 *   reads a form's input and stores it as a javascript
 *   object accessible through `req.body` 
 *
 * 'body-parser' must be installed (via `npm install --save body-parser`)
 * For more info see: https://github.com/expressjs/body-parser
 */
var bodyParser = require('body-parser');

// create our app
var app = express();

// instruct the app to use the `bodyParser()` middleware for all routes
app.use(bodyParser.urlencoded({ extended: true }));

// A browser's default method is 'GET', so this
// is the route that express uses when we visit
// our site initially.
app.get('/', function(req, res){

  // The form's action is '/' and its method is 'POST',
  // so the `app.post('/', ...` route will receive the
  // result of our form
  var html = '<form action="/" method="post">' +
               'Enter your name:' +
               '<input type="text" name="userName" placeholder="Put your name" />' +
               '<br>' +'Enter your city:'+'<input type="text" name="userCity" placeholder="Put your city" />' +
               '<br>' +'Enter your state:'+'<input type="text" name="userState" placeholder="Put your state" />' +
               '<br>' +'Enter your country:'+'<input type="text" name="userCountry" placeholder="Put your country" />' +
               '<br>' +
               '<button type="submit">Submit</button>' +
            '</form>';

  res.send(html);
});

// This route receives the posted form.
// As explained above, usage of 'body-parser' means
// that `req.body` will be filled in with the form elements
app.post('/', function(req, res){

  var userName = req.body.userName;
  var userCity = req.body.userCity;
  var userState = req.body.userState;
  var userCountry = req.body.userCountry;
 // var document = {userName:userName,userCity:userCity,userState:userState,userCountry:userCountry};
  var html = 'Hello: ' + userName + '.<br>' +'City: ' + userCity + '.<br>'+'State: ' + userState + '.<br>'+'country: ' + userCountry + '.<br>'+
             '<a href="/">Try again.</a>';
 // res.send(html);
//res.send(JSON.stringify(doc));
//lets require/import the mongodb native drivers.
var mongodb = require('mongodb');
var assert = require('assert');
var ObjectId = require('mongodb').ObjectID;
//We need to work with "MongoClient" interface in order to connect to a mongodb server.
var MongoClient = require('mongodb').MongoClient;

// Connection URL. This is where your mongodb server is running.
var url = 'mongodb://localhost:27017/test';

// Use connect method to connect to the Server
MongoClient.connect(url, function (err, db) {
  if (err) {
    console.log('Unable to connect to the mongoDB server. Error:', err);
  } else {
    //HURRAY!! We are connected. :)
   console.log('Connection established to', url);
   /* var userName = req.body.userName;
  var userCity = req.body.userCity;
  var userState = req.body.userState;
  var userCountry = req.body.userCountry;
    var document = {userName:userName, userCity:userCity,userState:userState,userCountry:userCountry};*/
    // do some work here with the database.

    var insertDocument = function(db, callback) {
   db.collection('test').insertOne( {
      "userName" :userName,
      "userCity" : userCity,
      "userState" : userState,
      "userCountry" :userCountry ,


   }, function(err, result) {
    assert.equal(err, null);
    console.log("Inserted a document into the test collection.");
    callback(result);
  });
};
    var findDocument = function(db, callback) {
   var cursor =db.collection('test').find( );
   cursor.each(function(err, doc) {
      assert.equal(err, null);
      if (doc != null) {
        console.log(doc);
      //  res.contentType('application/json');
res.send(JSON.stringify(doc));
     /*  app.get('/test', function(req, res, next) {
  res.json(doc);
});*/
      } else {
         callback();
      }
    //   res.send(JSON.stringify(doc));
   });

};


    MongoClient.connect(url, function(err, db) {
  assert.equal(null, err);
  insertDocument(db, function() {
     findDocument(db, function() {
      db.close();
  });
  });

});



   /* var document = {name:"David", title:"About MongoDB"};
db.collection('test').insertOne(document, function(err, records) {
        if (err) throw err;
        console.log("Record added as "+records[0]._id);
    });*/
    //Close connection
   // db.close();
  }
});
});
app.listen(3000);

请帮我解决问题。谢谢.. 我得到的错误是在发送后无法设置标题

Answer 1

这种错误通常意味着您尝试从同一路线多次使用res.send(...)。

您可以在查找文档中看到，您使用cursor.each，并将结果发送到此cursor.each。这意味着您从同一路线发送多个结果。

您应该做的是拥有一个变量，用于存储结果，然后在检索完所有内容后再发送结果。

node.js数据获取json模型错误

1 个答案: