我正在编写一个简单的查询来获取 mongodb 中的所有类(class)列表。我收到 {} 作为响应，node.js 停止并出现错误“错误:发送后无法设置 header 。”

这是我的类(class)集合架构。类(class).js

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

var course = new Schema({

course : [{courseName : String}]

}, {collection : 'course'});

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

这里是用于查询的 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)

请告诉我哪里出错了。

最佳答案

使用 express，每个路由只能调用一次 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，对吗？

您需要做的是先创建一个对象数组，然后返回它。

以下是修改现有路线以使其正常工作的方法:

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});
  });
});

关于javascript - Node.js 错误 : Can't set headers after they are sent.，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41584122/