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node.js - NodeJS/Mongo : Looping a query through various collections

转载 作者:IT老高 更新时间:2023-10-28 12:31:18 25 4
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我希望使用 NodeJS Driver 使用 MongoDB 通过各种集合循环查询。 .对于这个测试,我使用了 sample code from the 'findOne' docs在各种集合中插入一堆文档:

  collection.insertMany([{a:1, b:1}, {a:2, b:2}, {a:3, b:3}], {w:1}, function(err, result) {
test.equal(null, err);

同时创建各种集合(每个集合至少有一个先前插入的文档实例):

  • 测试
  • 测试1
  • 测试2
  • 测试3
  • 测试4
  • 测试6
  • 测试10

我想要的是收集我在数据库中的集合列表(在我的例子中是 'test'):

var MongoClient = require("mongodb").MongoClient,
test = require("assert");
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
db.listCollections().toArray(function(err, items) {
test.ok(items.length >= 1);
console.log(items);
db.close();
});
});

然后弹出前面提到的集合列表。到目前为止一切都很好!我什至可以遍历数组以仅获取集合的名称:

var MongoClient = require("mongodb").MongoClient,
test = require("assert");
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
db.listCollections().toArray(function(err, items) {
test.ok(items.length >= 1);
items.forEach(c => {
console.log(c.name);
});
db.close();
});
});

同样没有问题!但是当我在循环中尝试查询时:

var MongoClient = require("mongodb").MongoClient,
test = require("assert");
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
db.listCollections().toArray(function(err, items) {
test.ok(items.length >= 1);
items.forEach(c => {
var collection = db.collection(c.name);
collection.findOne({ a: 2 }, { fields: { b: 1 } }, function(err, doc) {
console.log(doc);
});
});
});
db.close();
});

我明白了:

null
null
null
null
null
null
null

即使循环获取集合似乎工作得很好:

var MongoClient = require("mongodb").MongoClient,
test = require("assert");
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
db.listCollections().toArray(function(err, items) {
test.ok(items.length >= 1);
items.forEach(c => {
var collection = db.collection(c.name);
console.log(collection);
});
});
db.close();
});

示例输出:

Collection {
s:
{ pkFactory:
{ [Function: ObjectID]
index: 10866728,
createPk: [Function: createPk],
createFromTime: [Function: createFromTime],
createFromHexString: [Function: createFromHexString],
isValid: [Function: isValid],
ObjectID: [Circular],
ObjectId: [Circular] },
db:
Db {
domain: null,
_events: {},
_eventsCount: 0,
_maxListeners: undefined,
s: [Object],
serverConfig: [Getter],
bufferMaxEntries: [Getter],
databaseName: [Getter] },
topology:
Server {
domain: null,
_events: [Object],
_eventsCount: 8,
_maxListeners: undefined,
clientInfo: [Object],
s: [Object] },
dbName: 'test',
options:
{ promiseLibrary: [Function: Promise],
readConcern: undefined,
readPreference: [Object] },
namespace: 'test.test2',
readPreference:
ReadPreference {
_type: 'ReadPreference',
mode: 'primary',
tags: undefined,
options: undefined },
slaveOk: true,
serializeFunctions: undefined,
raw: undefined,
promoteLongs: undefined,
promoteValues: undefined,
promoteBuffers: undefined,
internalHint: null,
collectionHint: null,
name: 'test2',
promiseLibrary: [Function: Promise],
readConcern: undefined } }

我猜 Collection 结构是我的循环的问题,但我不确定到底发生了什么......这是每个集合的预期输出示例:

{ _id: 5a13de85a55e615235f71528, b: 2 }

任何帮助将不胜感激!提前致谢!

最佳答案

虽然不是最好的语法并且除了记录输出之外没用,但这对我有用:

var mongodb = require('mongodb');


mongodb.connect('mongodb://localhost:27017/test', function (err, db) {
if (err) {
throw err;
}

db.listCollections().toArray(function (err, cols) {
if (err) {
throw err;
}

cols.forEach(function (col) {
db.collection(col.name).find({}, {}, 0, 1, function (err, docs) {
if(err){
throw err;
}
console.log(col);
docs.forEach(console.log);
});
});
})
})

那么,也许查询条件不匹配?

另外,使用 Promises 会更好:

const mongodb = require('mongodb');
const Promise = require('bluebird');

function getDb() {
return Promise.resolve(mongodb.connect('mongodb://localhost:27017/test'));
}

function getCollections(db) {
return Promise.resolve(db.listCollections().toArray());
}

function getDocs(db, col) {
return Promise.resolve(db.collection(col.name).find({},{},0,1).toArray());
}

const data = {};
getDb()
.then((db) => {
data.db = db;
return getCollections(db);
}).then((cols) => {
data.cols = cols;
return Promise.map(cols, (col) => getDocs(data.db,col));
}).then((docs) => {
console.log(docs);
})

关于node.js - NodeJS/Mongo : Looping a query through various collections,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/47408934/

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