Question

我正在尝试通过将Raspberry Pi 2与DietPi（DietPi v6.22.3），mongodb和nodejs结合使用，通过简单的mongo选择构建实时图表。

我想做的是使用类似的东西从数据库中获取数据：

var express = require('express');
var app = express();
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/DB_A';
var str = "";

app.route('/PAGE_A').get(function (req, res) {
    MongoClient.connect(url, function (err, db) {
        if (err) {
            console.log(err);
        } else {
            console.log("Connected to db");
            var cursor = db.collection('COL_A').find();
            console.log(cursor);
            //noinspection JSDeprecatedSymbols
            cursor.each(function (err, item) {
                if (item != null) {
                    str = str + "    DateTime  " + item.dt + " - Users:  " + item.users + " </br>";
                }
            });
            res.send(str);
            db.close();
        }
    });

});

var server = app.listen(8080, function () {});

运行节点app.js并访问指定的IP：8080 / page_A，我收到“ Connected to db”消息，但没有打印来自游标的预期数据，除了我用于此问题的参数外。集合不为空。我可以使用DB_A并从db.COL_A.find（）中获取元素。

这是我“ npm start”并访问IP / PAGE_A时在控制台上打印的内容：

Connected to db
Cursor {
  db:
   Db {
     _events: [Object: null prototype] {},
     _eventsCount: 0,
     _maxListeners: undefined,
     databaseName: 'DB_A',
     serverConfig:
      Server {
        _events: [Object: null prototype] {},
        _eventsCount: 0,
        _maxListeners: undefined,
        _callBackStore: [CallbackStore],
        host: 'localhost',
        port: 27017,
        options: [Object],
        internalMaster: true,
        connected: true,
        poolSize: 5,
        disableDriverBSONSizeCheck: false,
        slaveOk: undefined,
        _used: true,
        replicasetInstance: null,
        ssl: false,
        sslValidate: false,
        sslCA: null,
        sslCert: undefined,
        sslKey: undefined,
        sslPass: undefined,
        _readPreference: null,
        socketOptions: [Object],
        logger: [Object],
        eventHandlers: [Object],
        _serverState: 'connected',
        _state: [Object],
        recordQueryStats: false,
        db: [Circular],
        dbInstances: [Array],
        connectionPool: [EventEmitter],
        isMasterDoc: [Object] },
     options:
      { read_preference_tags: null,
        read_preference: 'primary',
        native_parser: false,
        readPreference: [ReadPreference],
        safe: false,
        w: 1 },
     _applicationClosed: false,
     native_parser: false,
     bsonLib:
      { Code: [Function: Code],
        Symbol: [Function: Symbol],
        BSON: [Function],
        DBRef: [Function: DBRef],
        Binary: [Function],
        ObjectID: [Function],
        Long: [Function],
        Timestamp: [Function],
        Double: [Function: Double],
        MinKey: [Function: MinKey],
        MaxKey: [Function: MaxKey] },
     bson: BSON {},
     bson_deserializer:
      { Code: [Function: Code],
        Symbol: [Function: Symbol],
        BSON: [Function],
        DBRef: [Function: DBRef],
        Binary: [Function],
        ObjectID: [Function],
        Long: [Function],
        Timestamp: [Function],
        Double: [Function: Double],
        MinKey: [Function: MinKey],
        MaxKey: [Function: MaxKey] },
     bson_serializer:
      { Code: [Function: Code],
        Symbol: [Function: Symbol],
        BSON: [Function],
        DBRef: [Function: DBRef],
        Binary: [Function],
        ObjectID: [Function],
        Long: [Function],
        Timestamp: [Function],
        Double: [Function: Double],
        MinKey: [Function: MinKey],
        MaxKey: [Function: MaxKey] },
     _state: 'connected',
     pkFactory:
      { [Function: ObjectID]
        index: 0,
        createPk: [Function: createPk],
        createFromTime: [Function: createFromTime],
        createFromHexString: [Function: createFromHexString] },
     forceServerObjectId: false,
     safe: false,
     notReplied: {},
     isInitializing: true,
     auths: [],
     openCalled: true,
     commands: [],
     logger:
      { error: [Function: error],
        log: [Function: log],
        debug: [Function: debug] },
     slaveOk: false,
     tag: 1554299599878,
     eventHandlers:
      { error: [],
        parseError: [],
        poolReady: [],
        message: [],
        close: [] },
     serializeFunctions: false,
     raw: false,
     recordQueryStats: false,
     retryMiliSeconds: 1000,
     numberOfRetries: 60,
     readPreference:
      ReadPreference { _type: 'ReadPreference', mode: 'primary', tags: undefined } },
  collection:
   Collection {
     db:
      Db {
        _events: [Object: null prototype] {},
        _eventsCount: 0,
        _maxListeners: undefined,
        databaseName: 'DB_A',
        serverConfig: [Server],
        options: [Object],
        _applicationClosed: false,
        native_parser: false,
        bsonLib: [Object],
        bson: BSON {},
        bson_deserializer: [Object],
        bson_serializer: [Object],
        _state: 'connected',
        pkFactory: [Function],
        forceServerObjectId: false,
        safe: false,
        notReplied: {},
        isInitializing: true,
        auths: [],
        openCalled: true,
        commands: [],
        logger: [Object],
        slaveOk: false,
        tag: 1554299599878,
        eventHandlers: [Object],
        serializeFunctions: false,
        raw: false,
        recordQueryStats: false,
        retryMiliSeconds: 1000,
        numberOfRetries: 60,
        readPreference: [ReadPreference] },
     collectionName: 'COL_A',
     internalHint: null,
     opts: {},
     slaveOk: false,
     serializeFunctions: false,
     raw: false,
     readPreference: 'primary',
     pkFactory:
      { [Function: ObjectID]
        index: 0,
        createPk: [Function: createPk],
        createFromTime: [Function: createFromTime],
        createFromHexString: [Function: createFromHexString] } },
  selector: {},
  fields: undefined,
  skipValue: 0,
  limitValue: 0,
  sortValue: undefined,
  hint: null,
  explainValue: undefined,
  snapshot: undefined,
  timeout: true,
  tailable: undefined,
  awaitdata: undefined,
  numberOfRetries: 5,
  currentNumberOfRetries: 5,
  batchSizeValue: 0,
  slaveOk: false,
  raw: false,
  read: 'primary',
  returnKey: undefined,
  maxScan: undefined,
  min: undefined,
  max: undefined,
  showDiskLoc: undefined,
  comment: undefined,
  tailableRetryInterval: 100,
  exhaust: false,
  partial: false,
  totalNumberOfRecords: 0,
  items: [],
  cursorId: Long { _bsontype: 'Long', low_: 0, high_: 0 },
  dbName: undefined,
  state: 0,
  queryRun: false,
  getMoreTimer: false,
  collectionName: 'DB_A.COL_A' }

以下是我的设置的一些详细信息：

mongod --version
db version v2.4.14

node --version
v10.15.3

NodeJS mongo driver -> 1.2.13

cat /etc/os-release
PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

cat /etc/debian_version
9.8

uname -a
Linux DietPi 4.14.98+ #1200 Tue Feb 12 20:11:02 GMT 2019 armv6l GNU/Linux

cat /proc/cpuinfo
processor       : 0
model name      : ARMv6-compatible processor rev 7 (v6l)
BogoMIPS        : 697.95
Features        : half thumb fastmult vfp edsp java tls
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x0
CPU part        : 0xb76
CPU revision    : 7

Hardware        : BCM2835
Revision        : 000e
Serial          : 00000000ce0ee037

谢谢。

Answer 1

如果您想要欲望结果，可以使用async await

MongoClient.connect(url,  async (err, db) => {
  if (err) {
    console.log(err);
  } else {
    console.log("Connected to db");
    var cursor = await db.collection("comments").find().toArray();
    console.log({ cursor });
    db.close();
  }
});

但是，如果您想在每种游标方法中使用游标类型，则不确定为什么不起作用还将mongodb版本"^3.2.2"更改为"^2.2.33"没事

如何从具有元素的集合中的MongoDB游标中获取值

1 个答案: