Node.js - TypeError: Nie można odczytać właściwości "readPreference" niezdefiniowanej

Question

Otrzymuję błąd typu podczas próby użycia metody agregującej mongodb w moim programie Node. Używam wersji 0.10.16 węzła i wersji mongodb mongodb-win32-x86_64-2.4.2.

Oto szczegóły moim stole 'relacji' w MongoDB - `

db.relation.find().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") 
} 

To wszystko szorstkie dane w powyższej tabeli (zbiórki MongoDB). Potrzebuję "grupy przez" w wyrażeniach sql na powyższej tabeli na podstawie "selectedoption" kolumny i po prostu trzeba na to liczyć. Tak więc wynik będzie liczony na danych "RCB", "CSK", "Mumbai". Oto mój węzeł przykładowy fragment, usunięto un-wymagane linie używam Server Express -

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'); 
    }); 
}); 

Powyższa linia -

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

daje mi następujący błąd w konsoli węzła

TypeError: Cannot read property 'readPreference' of undefined at Collection.aggregate (D:\mongo-js - 1\node_modules\mongodb\lib\mongodb\collection.js:1632:17)

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) 

- To działa dobrze w konsoli mongodb i daje mi następujące wyjście -

> 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 
} 

Byłbym wdzięczny za wszelkie wskazówki i wskazówki, aby rozwiązać ten problem.

Answer 1

Trzeba wdrożyć zwrotnego functionlike to:

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