Mongodb aggregation by day based on unix timestamp

Question

I have googled alot, but not found any helpful solution... I want to find total number of daily users. I have a collection named session_log having documents like following

{
    "_id" : ObjectId("52c690955d3cdd831504ce30"),
    "SORTID" : NumberLong(1388744853),
    "PLAYERID" : 3,
    "LASTLOGIN" : NumberLong(1388744461),
    "ISLOGIN" : 1,
    "LOGOUT" : NumberLong(1388744853)
}

I want to aggregate from LASTLOGIN...

This is my query:

db.session_log.aggregate(
    { $group : {
        _id: {
            LASTLOGIN : "$LASTLOGIN"
        },
        count: { $sum: 1 }
    }}
);

But it is aggregating by each login time, not by each day. Any help would be appreciated

Answer 1

MongoDB 4.0 and newer

Use $toDate

db.session_log.aggregate([
    { "$group": {
        "_id": {
            "$dateToString": {
                "format": "%Y-%m-%d",
                "date": {
                    "$toDate": { 
                        "$multiply": [1000, "$LASTLOGIN"]
                    }
                }
            }
        },
        "count": { "$sum": 1 }
    } }
])

or $convert

db.session_log.aggregate([
    { "$group": {
        "_id": {
            "$dateToString": {
                "format": "%Y-%m-%d",
                "date": {
                    "$convert": { 
                        "input":  { 
                            "$multiply": [1000, "$LASTLOGIN"] 
                        }, 
                        "to": "date"
                    }
                }
            }
        },
        "count": { "$sum": 1 }
    } }
])

---

MongoDB >= 3.0 and < 4.0:

db.session_log.aggregate([
    { "$group": {
        "_id": {
            "$dateToString": {
                "format": "%Y-%m-%d",
                "date": {
                    "$add": [
                        new Date(0), 
                        { "$multiply": [1000, "$LASTLOGIN"] }
                    ]
                }
            }
        },
        "count": { "$sum": 1 }
    } }
])

---

You would need to convert the LASTLOGIN field to a millisecond timestamp through multiplying the value by 1000

{ "$multiply": [1000, "$LASTLOGIN"] }

, then convert to a date

"$add": [
    new Date(0),
    { "$multiply": [1000, "$LASTLOGIN"] }
]

and this can be done in the $project pipeline by adding your milliseconds time to a zero-milliseconds Date(0) object, then extract $year, $month, $dayOfMonth parts from the converted date which you can then use in your $group pipeline to group the documents by the day.

You should thus change your aggregation pipeline to this:

var project = {
    "$project":{ 
        "_id": 0,
        "y": {
            "$year": {
                "$add": [
                    new Date(0),
                    { "$multiply": [1000, "$LASTLOGIN"] }
                ]
            }
        },
        "m": {
            "$month": {
                "$add": [
                    new Date(0),
                    { "$multiply": [1000, "$LASTLOGIN"] }
                ]
            }
        }, 
        "d": {
            "$dayOfMonth": {
                "$add": [
                    new Date(0),
                    { "$multiply": [1000, "$LASTLOGIN"] }
                ]
            }
        }
    } 
},
group = {   
    "$group": { 
        "_id": { 
            "year": "$y", 
            "month": "$m", 
            "day": "$d"
        },  
        "count" : { "$sum" : 1 }
    }
};

Running the aggregation pipeline:

db.session_log.aggregate([ project, group ])

would give the following results (based on the sample document):

{ "_id" : { "year" : 2014, "month" : 1, "day" : 3 }, "count" : 1 }

---

An improvement would be to run the above in a single pipeline as

var group = {   
    "$group": { 
        "_id": {    
            "year": {
                "$year": {
                    "$add": [
                        new Date(0),
                        { "$multiply": [1000, "$LASTLOGIN"] }
                    ]
                }
            },
            "mmonth": {
                "$month": {
                    "$add": [
                        new Date(0),
                        { "$multiply": [1000, "$LASTLOGIN"] }
                    ]
                }
            }, 
            "day": {
                "$dayOfMonth": {
                    "$add": [
                        new Date(0),
                        { "$multiply": [1000, "$LASTLOGIN"] }
                    ]
                }
            }
        },  
        "count" : { "$sum" : 1 }
    }
};

Running the aggregation pipeline:

db.session_log.aggregate([ group ])

---