blocks|key|2878930|text|您需要构造ObjectID，而不是将其作为字符串传递。像这样的东西应该是有效的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2878931|var+BSON+=+require('mongodb').BSONPure;
var+obj_id+=+BSON.ObjectID.createFromHexString("4fcfd7f246e1464d05000001");|code-block|syntax|javascript|2878932|然后，尝试在find/findOne中使用它。|2878933|编辑:正如Ohad在评论中指出的(感谢Ohad!)，你也可以使用：|offset|length|2878934|new+require('mongodb').ObjectID(req.params.id)|2878935|而不是上面概述的createFromHexString。|style|CODE|2878936|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/455262/ohad-kravchick^0|0|0|0|5|4|0|0|0|8|J|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|13|8|@]|9|@$K|14|L|15|1|16]]|A|$]]|$1|M|3|N|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|18|8|@$K|19|L|1A|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

You need to construct the ObjectID and not pass it in as a string. Something like this should work:

<pre><code>var BSON = require('mongodb').BSONPure;
var obj_id = BSON.ObjectID.createFromHexString("4fcfd7f246e1464d05000001");
</code></pre>

Then, try using that in your find/findOne.

Edit: As pointed out by <a href="https://stackoverflow.com/users/455262/ohad-kravchick">Ohad</a> in the comments (thanks Ohad!), you can also use: 

<pre><code>new require('mongodb').ObjectID(req.params.id)
</code></pre>

Instead of <code>createFromHexString</code> as outlined above.

blocks|key|3093071|text|这是因为mongo中的_id字段不是string类型(与您的req.params.id相同)。正如在其他答案中所建议的，您应该显式地转换它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3093072|试试mongoskin，你可以像node-mongodb-native驱动程序一样使用它，但要加点糖。例如：|3093073|//+connect+easier
var+db+=+require('mongoskin').mongo.db('localhost:27017/testdb?auto_reconnect');

//+collections
var+companies+=+db.collection('companies');

//+create+object+IDs
var+oid+=+db.companies.id(req.params.id);

//+some+nice+functions…
companies.findById();

//…+and+bindings
db.bind('companies',+{
++top10:+function(callback)+{
++++this.find({},+{limit:+10,+sort:+[['rating',+-1]]).toArray(callback);
++}+
});

db.companies.top10(printTop10);|code-block|syntax|javascript|3093074|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/kissjs/node-mongoskin^0|B|3|I|6|U|D|0|2|9|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@]|D|@$9|12|A|13|1|14]]|E|$]]|$1|H|3|I|5|J|7|15|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

That's because <code>_id</code> field in mongo isn't of <code>string</code> type (as your <code>req.params.id</code>). As suggested in other answers, you should explicitly convert it.

Try <a href="https://github.com/kissjs/node-mongoskin" rel="nofollow">mongoskin</a>, you could use it like node-mongodb-native driver, but with some sugar. For example:

<pre class="lang-js prettyprint-override"><code>// connect easier
var db = require('mongoskin').mongo.db('localhost:27017/testdb?auto_reconnect');

// collections
var companies = db.collection('companies');

// create object IDs
var oid = db.companies.id(req.params.id);

// some nice functions…
companies.findById();

//… and bindings
db.bind('companies', {
 top10: function(callback) {
 this.find({}, {limit: 10, sort: [['rating', -1]]).toArray(callback);
 } 
});

db.companies.top10(printTop10);
</code></pre>

blocks|key|222399|text|您可以使用findById()，它将为您处理id转换。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|222400|company+=+Company.findById(req.params.id,+function(err,+company)+{
++++//////////
});|code-block|syntax|javascript|222401|entityMap^0|5|A|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You can use <code>findById()</code> which will take care of the id conversion for you.

<pre><code>company = Company.findById(req.params.id, function(err, company) {
 //////////
});
</code></pre>

blocks|key|222403|text|如果这些对你不起作用，这对我访问博客帖子是有效的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|222404|const+getSinglePost+=+async+(req,+res)+=>+{

++++let+id+=+req.params.id;
++++var+ObjectId+=+require('mongodb').ObjectId;
++++const+db+=+await+client.db('CMS');

++++const+data+=+await+db.collection("posts").findOne({+_id:+ObjectId(id)+})

++++if+(data)+{
++++++++res.status(200).send(data)
++++}+else+res.status(400).send({+message:+"no+post+found"+})

}|code-block|syntax|javascript|222405|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In case these didn't work for you, this worked for me for accessing a blog post: 

<pre><code>const getSinglePost = async (req, res) =&gt; {

 let id = req.params.id;
 var ObjectId = require('mongodb').ObjectId;
 const db = await client.db('CMS');

 const data = await db.collection("posts").findOne({ _id: ObjectId(id) })

 if (data) {
 res.status(200).send(data)
 } else res.status(400).send({ message: "no post found" })

}
</code></pre>

I have a collection "companies" with several objects. Every object has "_id" parameter. I'm trying to get this parameter from db:

<pre><code>app.get('/companies/:id',function(req,res){
db.collection("companies",function(err,collection){
 console.log(req.params.id);
 collection.findOne({_id: req.params.id},function(err, doc) {
 if (doc){
 console.log(doc._id);
 } else {
 console.log('no data for this company');
 }
 });
});
});
</code></pre>

So, I request companies/4fcfd7f246e1464d05000001 (4fcfd7f246e1464d05000001 is _id-parma of a object I need) and findOne returns nothing, that' why console.log('no data for this company'); executes.

I'm absolutely sure that I have an object with _id="4fcfd7f246e1464d05000001". What I'm doing wrong? Thanks!

However, I've just noticed that id is not a typical string field. That's what mViewer shows:

<pre><code>"_id": {
 "$oid": "4fcfd7f246e1464d05000001"
 },
</code></pre>

Seems to be strange a bit...

NodeJS + MongoDB: Getting data from collection with findOne ()

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个"companies“集合，里面有几个对象。每个对象都有"_id“参数。我正在尝试从db获取此参数：app.get('/companies/:id',function(req,res){db.collection("companies",function(err,collection){    console....

问NodeJS + MongoDB:使用findOne ()从集合中获取数据
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