MongoDB group by date and fill zero counts - mongodb

Question

I would like to group my search results by date. The results are then also counted.
var fromDate = new Date(req.query.fromDate);
var toDate = new Date(req.query.toDate);
global.databaseStatistic.collection(global.ARTICLEPRESS).aggregate([
{
$match: {
article: { $in: articleIdArray },
date: { $gte: fromDate, $lte: toDate }
}
},
{
$group: {
"_id": {
"date": {
$dateToString: { format: "%d.%m.%Y", date: "$date" }
}
},
"count": { $sum: 1 }
}
}
])
This works perfectly, but I would also like to show all days that have a count of zero. It should be so displayed every day within an interval, also having a count of zero. How can I do that?

Answer 1

as it looks very trivial - it is not.
There is no way to have a reference sequence to compare with, even $lookup cannot help as this a kind of inner join type.
The way you could have this done is a kind of post process of result-set returned to mongoose.
The steps I have in mind could be:
create array of dates from req.query.fromDate to req.query.toDate formated in the same way as in query
remove entries in array which we have in result set
merge our array with count:0 and date
sort results (if needed)
any comments welcome!