Add support for db.collection.distinctDate

[quique0194]

Imagine you have a collection with a timestamp property, and you want to know quickly what dates are those object from.

I leave a piece of code to start here:

db.collection.aggregate([
    { "$project": {
         "year": { "$year": "$created" },
         "month": { "$month": "$created" },
         "day": { "$dayOfMonth": "$created" }
    }},
    { "$group": {
        "_id": null,
        "distinctDate": { "$addToSet": { "year": "$year", "month": "$month", "day": "$day" }}
    }}
])

It could also be possible to add a distinctAndCountDate shortcut, it would be extremely useful for some scenarios.