Question

我正在编写一个简单的查询来获取mongodb中的所有课程列表。我得到一个{}作为响应，node.js因错误而停止，“错误：发送后无法设置标题。”

这是我的课程集合架构。 course.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var course = new Schema({

course : [{courseName : String}]

}, {collection : 'course'});

module.exports = mongoose.model('course', course);

这是查询的index.js文件中的router.get。

router.get('/course', function (req, res) {

  collection = db.collection('course');
  query = {};
   projection = {"_id" : 0, "course.courseName": 1};

  cursor = collection.find(query);
  cursor.project(projection);
  cursor.forEach(function (doc) {
          res.send(doc);
      },
      function (err) {
          if(err)
              throw err;
      }
  );

});

这是我得到的错误。

GET /course 200 34.808 ms - 2
/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:175
  throw err;
  ^

Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:356:11)
at ServerResponse.header (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/express/lib/response.js:718:10)
at ServerResponse.send (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/express/lib/response.js:163:12)
at ServerResponse.json (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/express/lib/response.js:249:15)
at ServerResponse.send (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/express/lib/response.js:151:21)
at /home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/routes/index.js:234:19
at /home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/lib/cursor.js:773:23
at handleCallback (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:172:5)
at nextFunction (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:682:5)
at Cursor.next [as _next] (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:692:3)
at loop (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/lib/cursor.js:687:8)
at _each (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/lib/cursor.js:734:16)
at /home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/lib/cursor.js:745:7
at handleCallback (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/lib/utils.js:96:12)
at /home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/lib/cursor.js:675:5
at handleCallback (/home/vikas/study/angularjs/learnAngularjsCoursera/passportAuthentication/node_modules/mongodb/node_modules/mongodb-core/lib/cursor.js:172:5)

请建议我哪里出错了。

Answer 1

使用快递，您每条路线只能拨打一次res.send。在您的情况下，您似乎正在尝试将文档列表返回给客户端，对吗？

您需要做的是先创建一个对象数组，然后将其返回。

以下是如何修改现有路线以便正常工作的方法：

router.get('/course', function(req, res) {
  var collection = db.collection('course');
  var query = {};
  var projection = {"_id" : 0, "course.courseName": 1};
  var docs = [];

  cursor = collection.find(query);
  cursor.project(projection);

  cursor.forEach(function(doc) {
    docs.push(doc);
  }, function (err) {
    if (err) throw err;
    res.json({docs: docs});
  });
});

Answer 2

可以使用回调函数和return res.send尝试所有数据。

像：

router.get('/course', function (req, res) {

  var collection = db.collection('course');
  var query = {};
  var projection = {"_id" : 0, "course.courseName": 1};

  collection.find(query, projection).toArray(function (err, docs) {
      if(err) {
           return res.status(500).send({error:err.message});
      } 
      return res.status(200).send(docs);
  });

});

你可以根据你的问题描述使用猫鼬。所以你应该使用它而不是collection = db.collection('course');。首先加载course模型，然后使用

var Course = require("course");// your course.js file path. can be like: "../model/course"

Course.find(query, projection, function (err, docs){
//... like above function 
});

Node.js错误：发送后无法设置标头。

2 个答案: