How to count distinct date items in a timestamp field in Mongoose/NodeJS?

问题

I use Mongoose in my NodeJS, and I have a collection with documents that look like this -

var SomeSchema = new Schema({
    date: {
        type: Date,
        default: new Date()
    },
    some_item: {
        type: String
    }
});

The date field contains date with the time component (for example, 2014-05-09 09:43:02.478Z). How do I get a count of distinct items for a given date, say 2014-05-08?

EDIT: Ideally, I would like to get a count of records for each distinct date.

回答1:

What you want is usage of the aggregation framework with the aggregate() command, at least for finding one date as you ask:

SomeSchema.aggregate(
    [
        { "$match": {
            "date": { 
                "$gte": new Date("2014-05-08"), "$lt": new Date("2014-05-09")
            }
        }},
        { "$group": {
            "_id": "$some_item",
            "count": { "$sum": 1 }
        }}
    ],
    function(err,result) {
        // do something with result

    }
);

If you are specifically looking for "counts" over several dates then you can do something like this:

SomeSchema.aggregate(
    [
        { "$match": {
            "date": { 
                "$gte": new Date("2014-05-01"), "$lt": new Date("2014-06-01")
            }
        }},
        { "$group": {
            "_id": { 
                "year":  { "$year": "$date" },
                "month": { "$month": "$date" },
                "day":   { "$dayOfMonth": "$date" }
            }
            "count": { "$sum": 1 }
        }}
    ],
    function(err,result) {
        // do something with result

    }
);

And that gives you "per day" grouping. Look for the date aggregation operators in the documentation if you wish to take this further.

来源：https://stackoverflow.com/questions/23563289/how-to-count-distinct-date-items-in-a-timestamp-field-in-mongoose-nodejs