Tricky Mongoose Aggregation Query - node.js

Question

The following schema is given:
LogSchema {
...
likes: Number,
author: User,
created_at: Date
...
}
The following query seems to be very tricky:
Get the top X users who have the most likes for all today created logs.
The result should look like this:
User x: 1000 likes
User y: 558 likes
etc.
I have no clue how I can attack that. I know, that I could use some Aggregation, but how should it be done here, since likes are bound to users somehow.

Answer 1

Here is one example with commands .aggregate() used under Mongo Shell with test data
{ "_id" : ObjectId("56c912a1ebf94ca549e4ab8f"), "likes" : 123, "author" : "x", "created_at" : ISODate("2016-02-21T01:28:01.549Z") }
{ "_id" : ObjectId("56c912aaebf94ca549e4ab90"), "likes" : 120, "author" : "x", "created_at" : ISODate("2016-02-21T01:28:10.116Z") }
{ "_id" : ObjectId("56c912b4ebf94ca549e4ab91"), "likes" : 12, "author" : "y", "created_at" : ISODate("2016-02-21T01:28:20.996Z") }
{ "_id" : ObjectId("56c912bbebf94ca549e4ab92"), "likes" : 22, "author" : "y", "created_at" : ISODate("2016-02-21T01:28:27.644Z") }
Commands
> var d = new Date();
> d.setHours(0, 0, 0); // set to the first second of today, used for query today logs
> db.log.aggregate([
// query today logs by `create_at`
{$match: {created_at: {$gt: d}}},
// group by author and sum the `likes`
{$group: {_id: '$author', likes: {$sum: '$likes'}}}
]).map(function(val) {
// map the field per request
return {[val._id]: val.likes}
});
Result
[ { "y" : 34 }, { "x" : 243 } ]
With mongoose aggregate, please try it
var p = Log.aggregate([
// query today logs by `create_at`
{$match: {created_at: {$gt: d}}},
// group by author and sum the `likes`
{$group: {_id: '$author', likes: {$sum: '$likes'}}}
]).exec();
p.then(function(vals){
return vals.map(function(val) {
return {[val._id]: val.likes};
});
});