MongoDB Correct Schema for aggregated data

Question

I have a big collection that holds lots of stats, since I want to generate reports, I am running a daily cron which aggregates data from the main collection to a smaller one

Answer 1

Would recommend further restructuring the schema in Method 2 to follow this schema:

/* 0 */
{
    "_id" : ObjectId("5577fd322ab13c8cacdd0e70"),
    "order_id" : "VjprK",
    "user_id" : "777",
    "data" : [ 
        {
            "order_date" : ISODate("2015-04-18T08:57:42.514Z"),
            "amount" : 100
        }, 
        {
            "order_date" : ISODate("2015-04-19T08:57:42.514Z"),
            "amount" : 200
        }, 
        {
            "order_date" : ISODate("2015-04-20T08:57:42.514Z"),
            "amount" : 300
        }, 
        {
            "order_date" : ISODate("2015-04-21T08:57:42.514Z"),
            "amount" : 400
        }
    ]
}

which you can then aggregate with a given date range, say from 2015-04-18 to 2015-04-19. Consider the following pipeline:

var start = new Date(2015, 3, 18),
    end = new Date(2015, 3, 20);

db.orders.aggregate([
    {
        "$match": {
            "user_id": "777",
            "data.order_date": {
                "$gte": start,
                "$lt": end
            }
        }
    },
    {
        "$unwind": "$data"
    },
    {
        "$match": {
            "data.order_date": {
                "$gte": start,
                "$lt": end
            }
        }
    },
    {
        "$group": {
            "_id": "$user_id",
            "total": {
                "$sum": "$data.amount"
            }
        }
    }    
])

Sample Output

/* 0 */
{
    "result" : [ 
        {
            "_id" : "777",
            "total" : 300
        }
    ],
    "ok" : 1
}