blocks|key|2843715|text|选项2可能是最干净的。假设您有一个名为conn的Mongoose+Connection对象，该对象是使用mongoose.createConnection打开的，您可以通过conn.db访问原生mongo+Db对象。在那里，您可以调用collectionNames，它应该会提供您正在寻找的内容：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2843716|conn.db.collectionNames(function+(err,+names)+{
++++//+names+contains+an+array+of+objects+that+contain+the+collection+names
});|code-block|syntax|javascript|2843717|您还可以将集合名称作为参数传递给collectionNames，以便将结果过滤为您想要的结果。|2843718|Mongoose+4.x更新|BOLD|2843719|在Mongoos4.x使用的MongoDB本机驱动程序的2.x版本中，collectionNames已经被listCollections所取代，它接受一个过滤器并返回一个游标，所以你可以这样做：|2843720|mongoose.connection.db.listCollections({name:+'mycollectionname'})
++++.next(function(err,+collinfo)+{
++++++++if+(collinfo)+{
++++++++++++//+The+collection+exists
++++++++}
++++});|2843721|entityMap|0|LINK|mutability|MUTABLE|url|http://mongodb.github.com/node-mongodb-native/api-generated/db.html#collectionnames|1|http://mongodb.github.io/node-mongodb-native/2.0/api/Db.html#listCollections^0|J|4|X|A|1G|P|2E|7|2V|2|39|F|39|F|0|0|0|G|F|0|0|E|0|Z|F|1H|F|1H|F|1|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@$9|1G|A|1H|1|1I]]|E|$]]|$1|F|3|G|5|H|7|1J|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1K|8|@$9|1L|A|1M|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1N|8|@$9|1O|A|1P|B|O]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1Q|8|@$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@$9|1V|A|1W|1|1X]]|E|$]]|$1|R|3|S|5|H|7|1Y|8|@]|D|@]|E|$I|J]]|$1|T|3|-4|5|6|7|1Z|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]|11|$5|W|X|Y|E|$Z|12]]]]

Option 2 is probably the cleanest. Assuming you have a Mongoose <code>Connection</code> object named <code>conn</code> that's been opened using <code>mongoose.createConnection</code>, you can access the native mongo <code>Db</code> object via <code>conn.db</code>. From there you can call <a href="http://mongodb.github.com/node-mongodb-native/api-generated/db.html#collectionnames" rel="noreferrer"><code>collectionNames</code></a> which should provide what you're looking for:

<pre><code>conn.db.collectionNames(function (err, names) {
 // names contains an array of objects that contain the collection names
});
</code></pre>

You can also pass a collection name as a parameter to <code>collectionNames</code> to filter the results to just what you're looking for.

Mongoose 4.x Update

In the 2.x version of the MongoDB native driver that Mongoose 4.x uses, <code>collectionNames</code> has been replaced by <a href="http://mongodb.github.io/node-mongodb-native/2.0/api/Db.html#listCollections" rel="noreferrer"><code>listCollections</code></a> which accepts a filter and returns a cursor so you would do this as:

<pre><code>mongoose.connection.db.listCollections({name: 'mycollectionname'})
 .next(function(err, collinfo) {
 if (collinfo) {
 // The collection exists
 }
 });
</code></pre>

blocks|key|2843723|text|在集合列表中查找集合|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2843724|public+function+CollectionExists($collectionName)
++++{
++++++++$mongo+=+new+Mongo();
++++++++$collectionArr+=+$mongo->selectDB('yourrec')->listCollections();
++++++++if+(in_array($collectionName,+$collectionArr))+{
++++++++++++return+true;
++++++++}
++++++++return+false;
++++}|code-block|syntax|javascript|2843725|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|$]]

Find collection in collection's list

<pre><code>public function CollectionExists($collectionName)
 {
 $mongo = new Mongo();
 $collectionArr = $mongo-&gt;selectDB('yourrec')-&gt;listCollections();
 if (in_array($collectionName, $collectionArr)) {
 return true;
 }
 return false;
 }
</code></pre>

blocks|key|3056756|text|这适用于我(mongoose版本5.1.1)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3056757|const+mongoose+=+require('mongoose');
const+mongoURI+=+'mongodb://localhost:27017/mydb'
//+notice+the+mongoose.createConnection+instead+of+mongoose.connect
const+conn+=+mongoose.createConnection(mongoURI);
conn.on('open',+function+()+{
++++conn.db.listCollections().toArray(function+(err,+collectionNames)+{
++++++if+(err)+{
++++++++console.log(err);
++++++++return;
++++++}
++++++++console.log(collectionNames);
++++++++conn.close();
++++});
});|code-block|syntax|javascript|3056758|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|$]]

This works for me (mongoose version 5.1.1):

<pre><code>const mongoose = require('mongoose');
const mongoURI = 'mongodb://localhost:27017/mydb'
// notice the mongoose.createConnection instead of mongoose.connect
const conn = mongoose.createConnection(mongoURI);
conn.on('open', function () {
 conn.db.listCollections().toArray(function (err, collectionNames) {
 if (err) {
 console.log(err);
 return;
 }
 console.log(collectionNames);
 conn.close();
 });
});
</code></pre>

blocks|key|206894|text|这里有另一种选择(使用了一点express，但我认为没有它也很好)，这对我很有效。假设您导入了一个模型。并且，假设Blog是您的模型的名称。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|206895|const+app+=+express();
const+Blog+=+require('./models/blog');

app.post('/example',+(req,+res)+=>+{
++Blog.findOne({name:+'collectionname'})
++.then(result+=>+{
++++if(result)+{
++++++//If+it+exists
++++}
++})
})|code-block|syntax|javascript|206896|“”“|206897|result为null或object。|206898|entityMap^0|E|7|1L|4|0|0|0|0|6|7|4|C|6|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|P|$]]

Here's another option (with a little use of <code>express</code>, but I think it works fine without it) that worked for me. Suppose you imported a model. And, let's say <code>Blog</code> is the name of your model.
 
<pre><code>const app = express();
const Blog = require('./models/blog');

app.post('/example', (req, res) =&gt; {
 Blog.findOne({name: 'collectionname'})
 .then(result =&gt; {
 if(result) {
 //If it exists
 }
 })
})

</code></pre>
''' 
The <code>result</code> is either <code>null</code> or <code>object</code>.

I need to insert some data using mongoose but the name of the collection is provided by the user at the moment of the insertion, so I first have to check if the collection exists.

The way I know how to check if a collection exists is by querying the <code>system.namespaces</code> collection. I can see 3 possible approaches to doing that.

<ol>
<li>Find a way to query <code>system.namespaces</code> using mongoose (maybe defining a schema that matches the one in the db).</li>
<li>Getting some underlying node-mongodb-native object from mongoose and performing the query manually. In any case, this is something I would like to learn how to do.</li>
<li>Using a separate instance of a node-mongodb-native (or some other driver) to perform the query</li>
</ol>

Number <code>3</code> is the least elegant and the one i'm trying to avoid, I don't want to load another instance of the driver nor create a new connection when mongoose already created one.

I'm going to try number <code>1</code> after writing this. I just checked <code>system.namespaces</code> and the schema looks quite simple 

I'd still like to hear some opinions.

Thanks!

Node.js - Mongoose - Check if a collection exists

数据库

MongoDB

我需要使用mongoose插入一些数据，但是集合的名称是由用户在插入时提供的，因此我必须首先检查集合是否存在。我知道如何检查集合是否存在的方法是查询system.namespaces集合。我可以看到3种可能的方法来做到这一点。找到了一种使用mongoose查询system.namespaces的方法(也许可以定义一个与...

问Node.js - Mongoose -检查集合是否存在
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