blocks|key|382785|text|你想让query.observe()来做这个。假设您有一个带有标签字段的Posts集合，并且您希望在添加带有important标签的帖子时得到通知。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|382786|http://docs.meteor.com/#observe|382787|//+collection+of+posts+that+includes+array+of+tags
var+Posts+=+new+Meteor.Collection('posts');

//+DB+cursor+to+find+all+posts+with+'important'+in+the+tags+array.
var+cursor+=+Posts.find({tags:+'important'});

//+watch+the+cursor+for+changes
var+handle+=+cursor.observe({
++added:+function+(post)+{+...+},+//+run+when+post+is+added
++changed:+function+(post)+{+...+}+//+run+when+post+is+changed
++removed:+function+(post)+{+...+}+//+run+when+post+is+removed
});|code-block|syntax|javascript|382788|如果您想在post更改时在每个浏览器中执行某些操作，则可以在客户机上运行此代码。或者你可以在服务器上运行，如果你想在添加重要帖子时向团队发送一封电子邮件。|382789|请注意，added和removed指的是查询，而不是文档。如果您有一个现有的post文档并运行|382790|Posts.update(my_post_id,+{$addToSet:+{tags:+'important'}});|382791|这将触发“已添加”回调，因为帖子将被添加到查询结果中。|382792|entityMap|0|LINK|mutability|MUTABLE|url^0|3|F|10|5|1I|9|0|0|V|0|0|0|0|4|5|A|7|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|18|8|@]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|H|3|I|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1D|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|J|7|1J|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|1K|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|G]]]]

You want <code>query.observe()</code> for this. Say you have a <code>Posts</code> collection with a tags field, and you want to get notified when a post with the <code>important</code> tag is added.

<a href="http://docs.meteor.com/#observe" rel="noreferrer">http://docs.meteor.com/#observe</a>

<pre><code>// collection of posts that includes array of tags
var Posts = new Meteor.Collection('posts');

// DB cursor to find all posts with 'important' in the tags array.
var cursor = Posts.find({tags: 'important'});

// watch the cursor for changes
var handle = cursor.observe({
 added: function (post) { ... }, // run when post is added
 changed: function (post) { ... } // run when post is changed
 removed: function (post) { ... } // run when post is removed
});
</code></pre>

You can run this code on the client, if you want to do something in each browser when a post changes. Or you can run this on the server, if you want to say send an email to the team when an important post is added.

Note that <code>added</code> and <code>removed</code> refer to the query, not the document. If you have an existing post document and run

<pre><code>Posts.update(my_post_id, {$addToSet: {tags: 'important'}});
</code></pre>

this will trigger the 'added' callback, since the post is getting added to the query result.

blocks|key|598712|text|目前，Meteor在一个实例/进程上工作得很好。在这种情况下，所有查询都要经过这个实例，它可以将其广播回其他客户端。此外，它每10秒轮询一次MongoDB，以查看外部查询对数据库的更改。他们计划在1.0版本中提高可伸缩性，并希望允许多个实例通知每个实例有关更改的信息。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598713|另一方面，DerbyJS正在使用Redis+PubSub。|598714|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|$]]

Currently, Meteor really works well with one instance/process. In such case all queries are going through this instance and it can broadcast it back to other clients. Additional, it polls MongoDB every 10s for changes to the database which were done by outside queries. They are plans for 1.0 to improve the scalability and hopefully allow multiple instances to inform each one about changes.

DerbyJS on the other hand is using Redis PubSub.

I asked a question a few months ago, to which Meteor seems to have the answer.

<a href="https://stackoverflow.com/questions/5257177/which-if-any-of-the-nosql-databases-can-provide-stream-of-changes-to-a-query">Which, if any, of the NoSQL databases can provide stream of *changes* to a query result set?</a>

How does Meteor receive updates to the results of a MongoDB query?

Thanks,

Chris.

How does Meteor receive updates to the results of a MongoDB query?

数据库

服务器

MongoDB

Redis

几个月前我问过一个问题，Meteor似乎有答案。Meteor如何接收MongoDB查询结果的更新？谢谢,克里斯。

问Meteor如何接收MongoDB查询结果的更新？
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