How do I group by day/month in mongoDB? - mongodb

Question

Here's how one document looks like:
{
"login_Id": "c",
"name": "Abhishek Soni",
"location": "BLAHBLAH",
"work": [
{
"date":ISODate("2014-01-01"),
"total_time": 100,
},
{
"date":ISODate("2014-09-02"),
"total_time": 100,
},
{
"date":ISODate("2014-01-01"),
"total_time": 10,
},
]
}
What I want to do is to run a query that'll give an output like this:
{login_Id: 'c', work:{'01' : 110, '02': 100, ... and so on}}
Basically, I just want to group the work part month wise.
This is what I have tried:
db.employees.aggregate([
{
"$project": {
"_id": 0,
"login_Id": 1,
"time": {
"$sum": "$work.total_time"
}
}
},
{
"$group": {
"_id": {
"$dayOfYear": "$work.date"
},
"time": {
"$sum": "$work.total_time"
}
}
}
]);
But it outputs null. If I remove the group clause, I get the total sum (i.e., 210) What's wrong?

Answer 1

You can try below aggregation
db.collection.aggregate([
{ "$unwind": "$work" },
{ "$match": { "work.date": { "$type": "date" }}},
{ "$group": {
"_id": { "date": { "$dayOfMonth": "$work.date" }},
"time": { "$sum": "$work.total_time" },
"login_Id": { "$first": "$login_Id" }
}},
{ "$group": {
"_id": "$login_Id",
"data": {
"$push": {
"k": { "$toString": "$_id.date" },
"v": "$time"
}
}
}},
{ "$project": {
"work": { "$arrayToObject": "$data" },
"_id": 0,
"login_id": "$_id"
}}
])
Output
[
{
"login_id": "c",
"work": {
"1": 110,
"2": 100
}
}
]