在mongodb中，db.collection.find()的返回类型是什么？
在mongodb中，db.collection.find()的返回类型是什么？
我正在尝试读取来自mongodb连接的find函数的输出。\n我想将数据库的结果存储为JSON/Array，命名为result，如下所示：\n
collection= db.collection('users');
result =collection.find()。
\n目前使用这段代码，我得到了一些奇怪的长json输出：\n
{ db:
{ domain: null,
_events: {},
_maxListeners: 10,
databaseName: 'askr',
serverConfig:
{ domain: null,
_events: [Object],
_maxListeners: 10,
auth: [Getter],
_callBackStore: [Object],
_commandsStore: [Object],
_dbStore: [Object],
options: [Object],
_serverState: 'connected',
_haProcess: [Object],
servers: [Object],
strategyInstance: [Object],
emitOpen: false,
_state: [Object],
_currentServerChoice: 0,
socketTimeoutMS: [Getter/Setter],
_used: true,
logger: [Object] },
options:
{ read_preference_tags: null,
read_preference: 'primary',
url: 'mongodb://vishal:admin@ds055680.mongolab.com:55680/askr',
native_parser: true,
readPreference: [Object],
safe: false,
w: 1 },
_applicationClosed: false,
slaveOk: false,
bufferMaxEntries: -1,
native_parser: true,
bsonLib:
{ BSON: [Object],
Long: [Object],
ObjectID: [Object],
DBRef: [Object],
Code: [Object],
Timestamp: [Object],
Binary: [Object],
Double: [Object],
MaxKey: [Object],
MinKey: [Object],
Symbol: [Object] },
bson: { promoteLongs: true },
bson_deserializer:
{ Code: [Object],
Symbol: [Object],
BSON: [Object],
DBRef: [Object],
Binary: [Object],
ObjectID: [Object],
Long: [Object],
Timestamp: [Object],
Double: [Object],
MinKey: [Object],
MaxKey: [Object],
promoteLongs: true },
bson_serializer:
{ Code: [Object],
Symbol: [Object],
BSON: [Object],
DBRef: [Object],
Binary: [Object],
ObjectID: [Object],
Long: [Object],
Timestamp: [Object],
Double: [Object],
MinKey: [Object],
MaxKey: [Object],
promoteLongs: true },
_state: 'connected',
pkFactory:
{ [Function: ObjectID]
index: 14533369,
createPk: [Function: createPk],
createFromTime: [Function: createFromTime],
createFromHexString: [Function: createFromHexString],
isValid: [Function: isValid],
ObjectID: [Circular],
ObjectId: [Circular] },
forceServerObjectId: false,
safe: false,
notReplied: {},
isInitializing: true,
openCalled: true,
commands: [],
logger: { error: [Function], log: [Function], debug: [Function] },
tag: 1426645764322,
eventHandlers:
{ error: [],
parseError: [],
poolReady: [],
message: [],
close: [] },
serializeFunctions: false,
raw: false,
recordQueryStats: false,
retryMiliSeconds: 1000,
numberOfRetries: 60,
readPreference: { _type: 'ReadPreference', mode: 'primary', tags: undefined } },
collection:
{ db:
{ domain: null,
_events: {},
_maxListeners: 10,
databaseName: 'askr',
serverConfig: [Object],
options: [Object],
_applicationClosed: false,
slaveOk: false,
bufferMaxEntries: -1,
native_parser: true,
bsonLib: [Object],
bson: [Object],
bson_deserializer: [Object],
bson_serializer: [Object],
_state: 'connected',
pkFactory: [Object],
forceServerObjectId: false,
safe: false,
notReplied: {},
isInitializing: true,
openCalled: true,
commands: [],
logger: [Object],
tag: 1426645764322,
eventHandlers: [Object],
serializeFunctions: false,
raw: false,
recordQueryStats: false,
retryMiliSeconds: 1000,
numberOfRetries: 60,
readPreference: [Object] },
collectionName: 'users',
internalHint: null,
opts: {},
slaveOk: false,
serializeFunctions: false,
raw: false,
readPreference: { _type: 'ReadPreference', mode: 'primary', tags: undefined },
pkFactory:
{ [Function: ObjectID]
index: 14533369,
createPk: [Function: createPk],
createFromTime: [Function: createFromTime],
createFromHexString: [Function: createFromHexString],
isValid: [Function: isValid],
ObjectID: [Circular],
ObjectId: [Circular] },
serverCapabilities: undefined },
selector: {},
fields: undefined,
skipValue: 0,
limitValue: 0,
sortValue: undefined,
hint: null,
explainValue: undefined,
snapshot: undefined,
timeout: true,
tailable: undefined,
awaitdata: undefined,
oplogReplay: undefined,
numberOfRetries: 5,
currentNumberOfRetries: 5,
batchSizeValue: 0,
raw: false,
readPreference: { _type: 'ReadPreference', mode: 'primary', tags: undefined },
returnKey: undefined,
maxScan: undefined,
min: undefined,
max: undefined,
showDiskLoc: undefined,
comment: undefined,
tailableRetryInterval: 100,
exhaust: false,
partial: false,
slaveOk: false,
maxTimeMSValue: undefined,
connection: undefined,
transforms: undefined,
totalNumberOfRecords: 0,
items: [],
cursorId: { _bsontype: 'Long', low_: 0, high_: 0 },
dbName: undefined,
state: 0,
queryRun: false,
getMoreTimer: false,
collectionName: 'askr.users' }
问题的出现原因：
问题的出现是因为作者正在尝试使用Mondodb Client来执行查询操作，但是不清楚db.collection.find()方法的返回类型是什么。
解决方法：
为了解决这个问题，可以查看官方文档或者其他资源，以获取有关db.collection.find()方法的返回类型的信息。这样，作者就可以知道如何正确地使用返回的结果进行后续操作。
以下是解决方法的代码示例：
const MongoClient = require('mongodb').MongoClient;
const url = 'mongodb://localhost:27017';
const dbName = 'myproject';
MongoClient.connect(url, function(err, client) {
console.log("Connected successfully to server");
const db = client.db(dbName);
const collection = db.collection('mycollection');
// 使用db.collection.find()方法进行查询
const cursor = collection.find({});
// 打印查询结果的类型
console.log(typeof cursor); // 输出结果应该是object
client.close();
});
希望通过上述代码示例，作者可以获取到db.collection.find()方法的返回类型，并可以继续进行后续操作。
在MongoDB中，db.collection.find返回一个Cursor，它是一个指向查询结果集的指针。客户端可以通过迭代Cursor来检索结果。默认情况下，Cursor在10分钟的不活动后会超时。
如果你想要存储find()的结果，可以对其进行迭代。例如：
collection = db.collection('users');
result = collection.find().forEach(function(item){
//这里的item是记录，即你要对每条记录进行的操作。
})
需要将.forEach更改为.each，为什么呢？我是指的来自MongoDB的cursor.forEach方法；参见这里：docs.mongodb.org/manual/reference/method/cursor.forEach。
但是我得到了一个异常，显示"Object #<Cursor> has no method 'forEach'"。当我将forEach更改为.each，就没有问题了。
在这种情况下，我想知道你在Node中使用的npm模块是什么。因为Object.prototype.forEach也是标准的JavaScript函数。
var MongoClient = require('mongodb').MongoClient;
这似乎是对forEach的模块覆盖。无论如何，MongoDB的实现是通过collection.find({}).toArray(function(err, docs) { //docs是整个数组 });来实现的。更多信息请参见：npmjs.com/package/mongodb#find-all-documents
让我们在聊天中继续讨论。
