blocks|key|853429|text|执行多个查询，或者使用嵌入式文档，或者查看“数据库引用”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|853430|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Perform multiple queries or use embedded documents or look at "database references".

blocks|key|637043|text|试图加入MongoDB将违背使用MongoDB的目的。但是，您可以使用DBref并编写应用程序级别的代码(或库)，以便它自动为您获取这些引用。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|637044|或者，您可以更改您的模式并使用embedded+documents。|637045|您的最终选择是让事情完全保持原样，并执行两个查询。|637046|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mongodb.org/display/DOCS/Database%2BReferences#DatabaseReferences-DBRef|1|https://docs.mongodb.com/manual/core/data-model-design/#std-label-data-modeling-embedding^0|Z|5|0|0|F|I|1|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]]|C|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]]]

Trying to JOIN in MongoDB would defeat the purpose of using MongoDB. You could, however, use a <a href="http://www.mongodb.org/display/DOCS/Database+References#DatabaseReferences-DBRef" rel="nofollow noreferrer">DBref</a> and write your application-level code (or library) so that it automatically fetches these references for you.
Or you could alter your schema and use <a href="https://docs.mongodb.com/manual/core/data-model-design/#std-label-data-modeling-embedding" rel="nofollow noreferrer">embedded documents</a>.
Your final choice is to leave things exactly the way they are now and do two queries.

blocks|key|853513|text|一种解决方案是:在收款后文档中添加isAdmin:+0/1标志。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|853514|其他解决方案:使用DBrefs|853515|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|$]]

One solution: add isAdmin: 0/1 flag to your post collection document.

Other solution: use DBrefs

blocks|key|637115|text|正如前面提到的，在MongoDB中，您不能在集合之间进行连接。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|637116|对于您的示例，解决方案可能是：|637117|var+myCursor+=+db.users.find({admin:1});
var+user_id+=+myCursor.hasNext()+?+myCursor.next()+:+null;
db.posts.find({owner_id+:+user_id._id});|code-block|syntax|javascript|637118|请参阅参考手册-游标部分：http://es.docs.mongodb.org/manual/core/cursors/|offset|length|637119|另一种解决方案是将用户嵌入到帖子集合中，但我认为对于大多数web应用程序来说，出于安全原因，用户集合需要独立。Users集合可能具有角色、权限等。|637120|posts
{
+"content":"Some+content",
+"user":{"_id":"12345",+"admin":1},
+"via":"facebook"
},
{
+"content":"Some+other+content",
+"user":{"_id":"123456789",+"admin":0},
+"via":"facebook"
}|637121|然后：|637122|db.posts.find({user.admin:+1+});|637123|entityMap|0|LINK|mutability|MUTABLE|url|http://es.docs.mongodb.org/manual/core/cursors/^0|0|0|0|D|1B|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|15|8|@]|9|@$K|16|L|17|1|18]]|A|$]]|$1|M|3|N|5|6|7|19|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1B|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

As mentioned before in MongoDB you can't JOIN between collections.

For your example a solution could be:

<pre><code>var myCursor = db.users.find({admin:1});
var user_id = myCursor.hasNext() ? myCursor.next() : null;
db.posts.find({owner_id : user_id._id});
</code></pre>

See the reference manual - cursors section: <a href="http://es.docs.mongodb.org/manual/core/cursors/">http://es.docs.mongodb.org/manual/core/cursors/</a>

Other solution would be to embed users in posts collection, but I think for most web applications users collection need to be independent for security reasons. Users collection might have Roles, permissons, etc.

<pre><code>posts
{
 "content":"Some content",
 "user":{"_id":"12345", "admin":1},
 "via":"facebook"
},
{
 "content":"Some other content",
 "user":{"_id":"123456789", "admin":0},
 "via":"facebook"
}
</code></pre>

and then:

<pre><code>db.posts.find({user.admin: 1 });
</code></pre>

blocks|key|853621|text|这是你问题的答案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|853622|db.getCollection('users').aggregate([
++++{$match+:+{admin+:+1}},
++++{$lookup:+{from:+"posts",localField:+"_id",foreignField:+"owner_id",as:+"posts"}},
++++{$project+:+{
++++++++++++posts+:+{+$filter+:+{input+:+"$posts"++,+as+:+"post",+cond+:+{+$eq+:+['$$post.via'+,+'facebook']+}+}+},
++++++++++++admin+:+1

++++++++}}

])|code-block|syntax|javascript|853623|或者你可以选择mongodb组选项。|853624|db.getCollection('users').aggregate([
++++{$match+:+{admin+:+1}},
++++{$lookup:+{from:+"posts",localField:+"_id",foreignField:+"owner_id",as:+"posts"}},
++++{$unwind+:+"$posts"},
++++{$match+:+{"posts.via":"facebook"}},
++++{+$group+:+{
++++++++++++_id+:+"$_id",
++++++++++++posts+:+{$push+:+"$posts"}
++++}}
])|853625|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Here is answer for your question.

<pre><code>db.getCollection('users').aggregate([
 {$match : {admin : 1}},
 {$lookup: {from: "posts",localField: "_id",foreignField: "owner_id",as: "posts"}},
 {$project : {
 posts : { $filter : {input : "$posts" , as : "post", cond : { $eq : ['$$post.via' , 'facebook'] } } },
 admin : 1

 }}

])
</code></pre>

Or either you can go with mongodb group option.

<pre><code>db.getCollection('users').aggregate([
 {$match : {admin : 1}},
 {$lookup: {from: "posts",localField: "_id",foreignField: "owner_id",as: "posts"}},
 {$unwind : "$posts"},
 {$match : {"posts.via":"facebook"}},
 { $group : {
 _id : "$_id",
 posts : {$push : "$posts"}
 }}
])
</code></pre>

<pre><code>users
{
 "_id":"12345",
 "admin":1
},
{
 "_id":"123456789",
 "admin":0
}

posts
{
 "content":"Some content",
 "owner_id":"12345",
 "via":"facebook"
},
{
 "content":"Some other content",
 "owner_id":"123456789",
 "via":"facebook"
}
</code></pre>

Here is a sample from my mongodb. I want to get all the posts which has "via" attribute equal to "facebook" and posted by an admin ("admin":1). I couldn't figure out how to acquire this query. Since mongodb is not a relational database, I couldn't do a join operation. What could be the solution ?

MongoDB query multiple collections at once

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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users{ "_id":"12345", "admin":1},{ "_id":"123456789", "admin":0}posts{ "content":"Some content", "owner_id":"12345", "via":"facebook"},{ "content":"Some other c...

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