find size of dictonary in mongo
<p>I have a collection 'school', which contains two fields,standard and students(studying in that standard).I want to find the number students in a particular standard.</p>

<pre><code>The structure of school collection is:
    {
"_id" : ObjectId("5809cb458c392528de086601"),
"standard" : 'First',
"students":{
    '1':{name: 'Shawn','age': 6},
    '2':{name: 'Ryan','age': 5},
    '3':{name: 'Caoline','age': 6},
    '4':{name: 'Debian','age': 6},
    '5':{name: 'Zara','age': 5},
    }
}
</code></pre>

<p>I know the query to find a particular Standard (eg: 'First'). It would look like this: db.school.findOne({'standard':'First'})</p>

<p>But I don't know How to find the number of students for that standard.   Since students is a dictionary object. So my question is How to find the size of dictionary in MongoDb?</p>