MongoDB Count and groupby subdocument - mongodb

Question

I have the following document:
{
"id":1,
"url":"mysite.com",
"views":
[
{"ip":"1.1.1.1","date":"01-01-2015"},
{"ip":"2.2.2.2","date":"01-01-2015"},
{"ip":"1.1.1.1","date":"01-01-2015"},
{"ip":"1.1.1.1","date":"01-01-2015"}
]
}
If i want to count how many unique ips (groupBy), how can I do that with mongo?

Answer 1

Use the aggregation framework to get the desired result. The aggregation pipeline will have a $unwind operation as the first step which deconstructs the views array field from the input documents to output a document for each element. Each output document replaces the array with an element value. The next pipeline stage $group then groups the documents by the "views.ip" field, calculates the count field for each group, and outputs a document for each unique state.
The new per-ip documents have two fields: the _id field and the count field. The _id field contains the value of the unique IP address; i.e. the group by field. The count field is a calculated field that contains the total ip count per each unique IP. To calculate the value, $group uses the $sum operator to calculate the total number of IP addresses. So your final aggregation pipeline would look like this:
db.collection.aggregate([
{
"$unwind": "$views"
},
{
"$group": {
"_id": "$views.ip",
"count": {
"$sum": 1
}
}
}
])
Output:
/* 1 */
{
"result" : [
{
"_id" : "2.2.2.2",
"count" : 1
},
{
"_id" : "1.1.1.1",
"count" : 3
}
],
"ok" : 1
}
-- UPDATE --
To get the total of all unique IP's, you need another $group pipeline stage, this time the _id is null, that is you group all the documents from the previous pipeline stream into one, then use the same $sum operation on that group to get the total of the count. The aggregation pipeline would look like this in the end:
db.collection.aggregate([
{
"$unwind": "$views"
},
{
"$group": {
"_id": "$views.ip",
"count": {
"$sum": 1
}
}
},
{
"$group": {
"_id": null,
"total": {
"$sum": "$count"
}
}
}
])
Output:
/* 1 */
{
"result" : [
{
"_id" : null,
"total" : 4
}
],
"ok" : 1
}