How to join multiple collections with $lookup in mongodb
<p>I want to join more than two collections in MongoDB using the aggregate <code>$lookup</code>. Is it possible to join? Give me some examples.</p>

<p>Here I have three collections:</p>

<p><code>users</code>:</p>

<pre><code>{    
    "_id" : ObjectId("5684f3c454b1fd6926c324fd"),
    "email" : "admin@gmail.com",
    "userId" : "AD",
    "userName" : "admin"
}
</code></pre>

<p><code>userinfo</code>:</p>

<pre><code>{
    "_id" : ObjectId("56d82612b63f1c31cf906003"),
    "userId" : "AD",
    "phone" : "0000000000"
}
</code></pre>

<p><code>userrole</code>:</p>

<pre><code>{
    "_id" : ObjectId("56d82612b63f1c31cf906003"),
    "userId" : "AD",
    "role" : "admin"
}
</code></pre>