Sort sub-arrays in an Aggregate Result - mongodb

Question

I have three documents:
{
"id_user": "t57092501745ad6285ac58c22",
"name": "Day #1",
"date": {
"$date": "2016-04-21T20:50:00.190Z"
},
"text": "My text"
}
{
"id_user": "t57092501745ad6285ac58c22",
"name": "Day #2",
"date": {
"$date": "2016-04-22T20:50:00.190Z"
},
"text": "My text"
}
{
"id_user": "t57092501745ad6285ac58c22",
"name": "Day #3",
"date": {
"$date": "2016-04-22T20:51:00.190Z"
},
"text": "My text"
}
and I need to group these for day, so I do:
{
"$match": {
"id_user": "t57092501745ad6285ac58c22"
}
}, {
"$sort": {
"date": -1
}
}, {
"$group": {
"_id": {
$dayOfYear: "$date"
},
"data": {
"$push": {
"id_user": "$id_user",
"name": "$name",
"date": "$date",
"text": "$text"
},
},
}
}
and the result is:
{
{
_id: 113,
data: [{
"id_user": "t57092501745ad6285ac58c22",
name: "Day #1",
date: "2016-04-22T20:51:00.190Z",
text: "My text"
}]
}, {
_id: 114,
data: [{
"id_user": "t57092501745ad6285ac58c22",
name: "Day #3",
date: "2016-04-23T20:51:00.190Z",
text: "My text"
}, {
"id_user": "t57092501745ad6285ac58c22",
name: "Day #2",
date: "2016-04-23T20:50:00.190Z",
text: "My text"
}]
}
}
and it's ok, but the order is not what I need:
{ Day #1 }, { Day #3, Day #2 }
if I change the sort to { "date": 1 } I can invert the order of the 2 groups, this way:
{ Day #3, Day #2 }, { Day #1 }
but I don't know how tho change also the order inside the sub-array, to obtain the correct:
{ Day #1 }, { Day #2, Day #3 }
What's the correct way?

Answer 1

If you want the items in the "array" to be in "ascending" order, then your $sort order is wrong, and you need to reverse it. Also output from $group as a "document" is not ordered in any way. So if you want a specific order then you need to actually $sort on the returned _id as well:
[
{ "$match": {
"id_user": "t57092501745ad6285ac58c22"
}},
{ "$sort": { "date": 1 } }
{ "$group": {
"_id": { "$dayOfYear": "$date" },
"data": {
"$push": {
"id_user": "$id_user",
"name": "$name",
"date": "$date",
"text": "$text"
}
}
}},
{ "$sort": { "_id": 1 } }
]
Then both orders are then correct