问mongodb检查是否存在值(node.js)
EN

Stack Overflow用户

提问于 2015-03-30 11:57:13

回答 1查看 11K关注 0票数 5

我使用Node.js和Mongo(mongodb驱动程序)向集合添加项。我有一个html站点，它使用socket.io将信息传递给页面。我可以插入到db中，但是当我试图查看值是否存在时，我会从Mongo得到一个奇怪的返回。我发送了一个名字，并试图把它放在客户的集合。到目前为止，我得到的是：

socket.on('DB', function(msg)
    {
        if(msg.Status == "Read")
        {
            MongoClient.connect(url, function(err, db)  //connect to mongo
            {
                var collection = db.collection('Clients');  // get reference to the collection
                collection.find(({Name: msg.Name},{$exists: true}), function(err, doc) //find if a value exists
                {     
                    if(doc) //if it does
                    {
                        console.log(doc); // print out what it sends back
                    }
                    else if(!doc) // if it does not 
                    {
                        console.log("Not in docs");
                    }
                });
              db.close();
            });

            }
}

这会让我觉得：

{ connection: null,
  server: null,
  disconnectHandler:
   { s: { storedOps: [], storeOptions: [Object], topology: [Object] },
     length: [Getter] },
  bson: {},
  ns: 'DB.Clients',
  cmd:
   { find: 'DB.Clients',
     limit: 0,
     skip: 0,
     query: { '$exists': true },
     slaveOk: true,
     readPreference: { preference: 'primary', tags: undefined, options: undefined } },
  options:
   { skip: 0,
     limit: 0,
     raw: undefined,
     hint: null,
     timeout: undefined,
     slaveOk: true,
     readPreference: { preference: 'primary', tags: undefined, options: undefined },
     db:
      { domain: null,
        _events: {},
        _maxListeners: 10,
        s: [Object],
        serverConfig: [Getter],
        bufferMaxEntries: [Getter],
        databaseName: [Getter],
        options: [Getter],
        native_parser: [Getter],
        slaveOk: [Getter],
        writeConcern: [Getter] },
     disconnectHandler: { s: [Object], length: [Getter] } },
  topology:
   { domain: null,
     _events:
      { reconnect: [Function],
        timeout: [Object],
        error: [Object],
        close: [Object],
        destroy: [Object] },
     _maxListeners: 10,
     s:
      { options: [Object],
        callbacks: [Object],
        logger: [Object],
        state: 'connected',
        reconnect: true,
        reconnectTries: 30,
        reconnectInterval: 1000,
        emitError: true,
        currentReconnectRetry: 30,
        ismaster: [Object],
        readPreferenceStrategies: undefined,
        authProviders: [Object],
        id: 5,
        tag: undefined,
        disconnectHandler: [Object],
        wireProtocolHandler: {},
        Cursor: [Object],
        bsonInstance: {},
        bson: {},
        pool: [Object],
        serverDetails: [Object] },
     name: [Getter],
     bson: [Getter],
     wireProtocolHandler: [Getter],
     id: [Getter] },
  cursorState:
   { cursorId: null,
     documents: [],
     cursorIndex: 0,
     dead: false,
     killed: false,
     init: false,
     notified: false,
     limit: 0,
     skip: 0,
     batchSize: 1000,
     currentLimit: 0,
     transforms: undefined },
  callbacks: null,
  logger: { className: 'Cursor' },
  _readableState:
   { highWaterMark: 16384,
     buffer: [],
     length: 0,
     pipes: null,
     pipesCount: 0,
     flowing: false,
     ended: false,
     endEmitted: false,
     reading: false,
     calledRead: false,
     sync: true,
     needReadable: false,
     emittedReadable: false,
     readableListening: false,
     objectMode: true,
     defaultEncoding: 'utf8',
     ranOut: false,
     awaitDrain: 0,
     readingMore: false,
     decoder: null,
     encoding: null },
  readable: true,
  domain: null,
  _events: {},
  _maxListeners: 10,
  s:
   { maxTimeMS: null,
     numberOfRetries: 5,
     tailableRetryInterval: 500,
     currentNumberOfRetries: 5,
     state: 0,
     streamOptions: {},
     bson: {},
     ns: 'DB.Clients',
     cmd:
      { find: 'DB.Clients',
        limit: 0,
        skip: 0,
        query: [Object],
        slaveOk: true,
        readPreference: [Object] },
     options:
      { skip: 0,
        limit: 0,
        raw: undefined,
        hint: null,
        timeout: undefined,
        slaveOk: true,
        readPreference: [Object],
        db: [Object],
        disconnectHandler: [Object] },
     topology:
      { domain: null,
        _events: [Object],
        _maxListeners: 10,
        s: [Object],
        name: [Getter],
        bson: [Getter],
        wireProtocolHandler: [Getter],
        id: [Getter] },
     topologyOptions:
      { socketOptions: {},
        auto_reconnect: true,
        host: 'localhost',
        port: 27017,
        cursorFactory: [Object],
        reconnect: true,
        emitError: true,
        size: 5,
        disconnectHandler: [Object],
        bson: {},
        messageHandler: [Function],
        wireProtocolHandler: {} } },
  timeout: false,
  sortValue: undefined,
  readPreference: { preference: 'primary', tags: undefined, options: undefined } }

，并且无论是否存在具有名称的文档，当我在cli中运行它时，它都会返回。

> db.Clients.find({Name: 'say what'}, {$exists: true})
{ "_id" : ObjectId("5519a66eb85de65c121182d9") }

这表明文档是存在的，如果我对一个不是mongo的文档运行相同的cmd，它将什么也不返回。是否在返回语句中找到一个引用，说明文档是否存在？

node.js

mongodb

javascript

回答 1

Stack Overflow用户

回答已采纳

发布于 2015-03-30 12:09:04

MongoDB find()方法向匹配查询条件的文档返回cursor。所以您在console.log(doc)中看到的实际上是返回的游标。当find()方法“返回文档”时，该方法实际上是将光标返回到文档。

您需要将一个toArray()方法添加到来自find()方法的结果游标中。

var collection = db.collection('Clients');  // get reference to the collection
collection.find({Name: msg.Name}, {$exists: true}).toArray(function(err, docs) //find if documents that satisfy the criteria exist
{     
    if(docs.length > 0) //if exists
    {
        console.log(docs); // print out what it sends back
    }
    else // if it does not 
    {
        console.log("Not in docs");
    }
});