Node.js – TypeError:无法读取未定义的属性'readPreference'

我正在尝试在我的Node程序中使用MongoDB的聚合方法时出现types错误。 我正在使用节点0.10.16版本和mongodb mongodb-win32-x86_64-2.4.2版本。

这里是我在MongoDB中的“关系”表的细节

db.relation.find()。的forEach(printjson)

{ "_id" : ObjectId("518808811189128048034c7b") } { "username" : "51880fa37901642c36000001", "selectedoption" : "RCB", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("5188137dee3a599c34000001") } { "username" : "51880fa37901642c36000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("518c2bd0afa8d2e82b000001") } { "username" : "51880fa37901642c36000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("518c2c81681aae0838000001") } { "username" : "51880fa37901642c36000001", "selectedoption" : "RCB", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("518c2c90681aae0838000002") } { "username" : "51880fa37901642c36000001", "selectedoption" : "CSK", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("518c2cefc7dc797c08000001") } { "username" : "51880fa37901642c36000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("518c2d48a2afbdc426000001") } { "username" : "51880fa37901642c36000001", "selectedoption" : "RCB", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("518c2e2fa2afbdc426000002") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "RCB", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fda9ea6abb63037000002") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "CSK", "question" : "who will IPL this year?", "_id" : ObjectId("521fdb3ba6abb63037000003") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fde8da6abb63037000004") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "CSK", "question" : "who will IPL this year?", "_id" : ObjectId("521fdef0a6abb63037000005") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fdf1aa6abb63037000006") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "RCB", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fdffe257b59cc3f000001") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fe09c827ff1e418000001") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "CSK", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fe0cb5022f0c03c000001") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "Mumbai", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fe1558b82555c25000001") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "CSK", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fe17d8b82555c25000002") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "CSK", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fe2e8c134b7bc40000001") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "CSK", "question" : "who will IPL this year?", "_id" : ObjectId("521fe354b59421cc07000001") } { "username" : "521fda91a6abb63037000001", "selectedoption" : "RCB", "question" : "Which team is going to win IPL6?", "_id" : ObjectId("521fe392b59421cc07000002") } 

这是上表中所有粗糙的数据(在MongoDB中收集)。 在“selectedoption”列的基础上,我需要在上面的表中以sql语言“group by”,并且只需要对此进行计数。 所以结果将会是“RCB”,“CSK”,“孟买”数据。 这里是我的示例节点片段,删除了不需要的行,我正在使用快递服务器 –

 var express = require('express'), routes = require('./routes'), user = require('./routes/user'), http = require('http'), path = require('path'); var app = express(); var mongo = require('mongodb'); var db = new mongo.Db('voteapp', new mongo.Server("127.0.0.1", 27017, { auto_reconnect: true }, { safe: false, strict: false })) app.get('/test', function(req, res) { res.send('works'); db.collection('relation', function(err, collection){ console.log('in'); collection.aggregate({$group : {_id: "$selectedoption", selectedoption: {$sum: 1}}}); console.log('out'); }); }); 

以上线 –

collection.aggregate({$ group:{_id:“$ selectedoption”,selectedoption:{$ sum:1}}})

给我在节点控制台中的以下错误

TypeError: 无法在Collection.aggregate (D:\ mongo-js-1 \ node_modules \ mongodb \ lib \ mongodb \ collection.js:1632:17) 读取undefined属性'readPreference'

 at D:\mongo-js - 1\app.js:107:16 at Db.collection (D:\mongo-js - 1\node_modules\mongodb\lib\mongodb\db.js:461:44) at D:\mongo-js - 1\app.js:105:6 at callbacks (D:\mongo-js - 1\node_modules\express\lib\router\index.js:161:37) at param (D:\mongo-js - 1\node_modules\express\lib\router\index.js:135:11) at pass (D:\mongo-js - 1\node_modules\express\lib\router\index.js:142:5) at Router._dispatch (D:\mongo-js - 1\node_modules\express\lib\router\index.js:170:5) at Object.router (D:\mongo-js - 1\node_modules\express\lib\router\index.js:33:10) at next (D:\mongo-js - 1\node_modules\express\node_modules\connect\lib\proto.js:190:15) 

– 在mongodb控制台运行良好,并给我以下输出 –

 > db.relation.aggregate({$group : {_id: "$selectedoption", selectedoption: {$sum: 1}}}); { "result" : [ { "_id" : "CSK", "selectedoption" : 9 }, { "_id" : "Mumbai", "selectedoption" : 10 }, { "_id" : "RCB", "selectedoption" : 8 }, { "_id" : null, "selectedoption" : 1 } ], "ok" : 1 } 

我真的很感激任何指针或指导来解决这个问题。

你需要像这样实现一个callback函数:

 collection.aggregate({$group : {_id: "$selectedoption", selectedoption: {$sum: 1}}}, function(err, result){ //some stuff });