blocks|key|625774|text|或者，您可以使用标准的Mongo方法，并在回调中，在运行回调时激发EventEmitter事件(在Node中)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|625775|侦听此事件的应用程序或体系结构的任何其他部分都将收到更新通知，以及发送到那里的任何相关数据。这是从Mongo获取通知的一种非常简单的方法。|625776|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Alternatively, you could use the standard Mongo FindAndUpdate method, and within the callback, fire an EventEmitter event (in Node) when the callback is run.

Any other parts of the application or architecture listening to this event will be notified of the update, and any relevant data sent there also. This is a really simple way to achieve notifications from Mongo.

blocks|key|410674|text|这里有一个可用的java示例，可以在here上找到。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|410675|+MongoClient+mongoClient+=+new+MongoClient();
++++DBCollection+coll+=+mongoClient.getDatabase("local").getCollection("oplog.rs");

++++DBCursor+cur+=+coll.find().sort(BasicDBObjectBuilder.start("$natural",+1).get())
++++++++++++.addOption(Bytes.QUERYOPTION_TAILABLE+%7C+Bytes.QUERYOPTION_AWAITDATA);

++++System.out.println("==+open+cursor+==");

++++Runnable+task+=+()+->+{
++++++++System.out.println("\tWaiting+for+events");
++++++++while+(cur.hasNext())+{
++++++++++++DBObject+obj+=+cur.next();
++++++++++++System.out.println(+obj+);

++++++++}
++++};
++++new+Thread(task).start();|code-block|syntax|javascript|410676|这里给出的关键是QUERY+OPTIONS。|410677|如果不需要每次都加载所有数据，您还可以更改查找查询。|410678|BasicDBObject+query=+new+BasicDBObject();
query.put("ts",+new+BasicDBObject("$gt",+new+BsonTimestamp(1471952088,+1))); //timestamp+is+within+some+range
query.put("op",+"i");+//Only+insert+operation

DBCursor+cur+=+coll.find(query).sort(BasicDBObjectBuilder.start("$natural",+1).get())
.addOption(Bytes.QUERYOPTION_TAILABLE+%7C+Bytes.QUERYOPTION_AWAITDATA);|410679|entityMap|0|LINK|mutability|MUTABLE|url|http://tugdualgrall.blogspot.fr/2015/01/how-to-create-pubsub-application-with.html|1|https://api.mongodb.com/java/3.1/com/mongodb/Bytes.html#QUERYOPTION_AWAITDATA^0|I|4|0|0|0|8|D|1|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|K|3|L|5|6|7|17|8|@]|9|@]|C|$]]|$1|M|3|N|5|F|7|18|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|19|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]]]

There is an working java example which can be found <a href="http://tugdualgrall.blogspot.fr/2015/01/how-to-create-pubsub-application-with.html" rel="nofollow">here</a>.

<pre><code> MongoClient mongoClient = new MongoClient();
 DBCollection coll = mongoClient.getDatabase("local").getCollection("oplog.rs");

 DBCursor cur = coll.find().sort(BasicDBObjectBuilder.start("$natural", 1).get())
 .addOption(Bytes.QUERYOPTION_TAILABLE | Bytes.QUERYOPTION_AWAITDATA);

 System.out.println("== open cursor ==");

 Runnable task = () -&gt; {
 System.out.println("\tWaiting for events");
 while (cur.hasNext()) {
 DBObject obj = cur.next();
 System.out.println( obj );

 }
 };
 new Thread(task).start();
</code></pre>

The key is <a href="https://api.mongodb.com/java/3.1/com/mongodb/Bytes.html#QUERYOPTION_AWAITDATA" rel="nofollow">QUERY OPTIONS</a> given here.

Also you can change find query, if you don't need to load all the data every time.

<pre><code>BasicDBObject query= new BasicDBObject();
query.put("ts", new BasicDBObject("$gt", new BsonTimestamp(1471952088, 1))); //timestamp is within some range
query.put("op", "i"); //Only insert operation

DBCursor cur = coll.find(query).sort(BasicDBObjectBuilder.start("$natural", 1).get())
.addOption(Bytes.QUERYOPTION_TAILABLE | Bytes.QUERYOPTION_AWAITDATA);
</code></pre>

blocks|key|625824|text|实际上，当使用mongoose+schema提供的中间件插入一些新的东西时，您为什么没有注意到，而不是查看输出|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|625825|您可以捕获插入新文档的事件，并在此插入完成后执行某些操作|625826|entityMap|0|LINK|mutability|MUTABLE|url|http://mongoosejs.com/docs/middleware.html^0|7|F|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Actually, instead of watching output, why you dont get notice when something new is inserted by using middle-ware that was provided by <a href="http://mongoosejs.com/docs/middleware.html" rel="nofollow noreferrer">mongoose schema</a> 

You can catch the event of insert a new document and do something after this insertion done

blocks|key|625884|text|从MongoDB+3.6开始，将有一个新的通知应用程序接口，称为Change+Streams，您可以使用它来实现这一点。参见this+blog+post+for+an+example。其中的示例如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|625885|cursor+=+client.my_db.my_collection.changes([
++++{'$match':+{
++++++++'operationType':+{'$in':+['insert',+'replace']}
++++}},
++++{'$match':+{
++++++++'newDocument.n':+{'$gte':+1}
++++}}
])

#+Loops+forever.
for+change+in+cursor:
++++print(change['newDocument'])|code-block|syntax|javascript|625886|entityMap|0|LINK|mutability|MUTABLE|url|https://emptysqua.re/blog/driver-features-for-mongodb-3-6/^0|1Q|T|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Since MongoDB 3.6 there will be a new notifications API called Change Streams which you can use for this. See <a href="https://emptysqua.re/blog/driver-features-for-mongodb-3-6/" rel="noreferrer">this blog post for an example</a>. Example from it:

<pre><code>cursor = client.my_db.my_collection.changes([
 {'$match': {
 'operationType': {'$in': ['insert', 'replace']}
 }},
 {'$match': {
 'newDocument.n': {'$gte': 1}
 }}
])

# Loops forever.
for change in cursor:
 print(change['newDocument'])
</code></pre>

blocks|key|410806|text|MongoDB版本3.6现在包括变更流，它本质上是OpLog之上的一个应用编程接口，允许类似触发/通知的用例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|410807|下面是一个Java例子的链接：http://mongodb.github.io/mongo-java-driver/3.6/driver/tutorials/change-streams/|offset|length|410808|NodeJS示例可能如下所示：|410809|+var+MongoClient+=+require('mongodb').MongoClient;
++++MongoClient.connect("mongodb://localhost:22000/MyStore?readConcern=majority")
+++++.then(function(client){
+++++++let+db+=+client.db('MyStore')

+++++++let+change_streams+=+db.collection('products').watch()
++++++++++change_streams.on('change',+function(change){
++++++++++++console.log(JSON.stringify(change));
++++++++++});
++++++});|code-block|syntax|javascript|410810|entityMap|0|LINK|mutability|MUTABLE|url|http://mongodb.github.io/mongo-java-driver/3.6/driver/tutorials/change-streams/^0|0|F|27|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

MongoDB version 3.6 now includes change streams which is essentially an API on top of the OpLog allowing for trigger/notification-like use cases. 

Here is a link to a Java example:
<a href="http://mongodb.github.io/mongo-java-driver/3.6/driver/tutorials/change-streams/" rel="noreferrer">http://mongodb.github.io/mongo-java-driver/3.6/driver/tutorials/change-streams/</a>

A NodeJS example might look something like:

<pre><code> var MongoClient = require('mongodb').MongoClient;
 MongoClient.connect("mongodb://localhost:22000/MyStore?readConcern=majority")
 .then(function(client){
 let db = client.db('MyStore')

 let change_streams = db.collection('products').watch()
 change_streams.on('change', function(change){
 console.log(JSON.stringify(change));
 });
 });
</code></pre>

I'm creating a sort of background job queue system with MongoDB as the data store. How can I &quot;listen&quot; for inserts to a MongoDB collection before spawning workers to process the job?
Do I need to poll every few seconds to see if there are any changes from last time, or is there a way my script can wait for inserts to occur?
This is a PHP project that I am working on, but feel free to answer in Ruby or language agnostic.

How to listen for changes to a MongoDB collection?

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我正在创建一种使用MongoDB作为数据存储的后台作业队列系统。在派生工作线程来处理作业之前，我如何“监听”MongoDB集合中的插入？我是否需要每隔几秒钟轮询一次，以查看与上次相比是否有任何更改，或者有没有一种方法可以让我的脚本等待插入发生？这是一个我正在做的PHP项目，但是你可以用Ruby或者语言不可知的语言来回答...

问如何侦听MongoDB集合的更改？
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