MongoDB sort documents by specified element in array - mongodb

Question

I have a collection like that:
[
{
student: "a",
package: [
{name: "one", createdAt: "2021-10-12T00:00:00", active: true},
{name: "two", createdAt: "2021-10-13T00:00:00", active: false},
{name: "three", createdAt: "2021-10-14T00:00:00", active: false}
]
},
{
student: "b",
package: [
{name: "one", createdAt: "2021-10-16T00:00:00", active: true},
{name: "two", createdAt: "2021-10-17T00:00:00", active: false},
{name: "three", createdAt: "2021-10-18T00:00:00", active: false}
]
},
{
student: "c",
package: [
{name: "one", createdAt: "2021-10-10T00:00:00", active: true},
{name: "two", createdAt: "2021-10-17T00:00:00", active: false},
{name: "three", createdAt: "2021-10-18T00:00:00", active: false}
]
}
]
I have no idea how can I do a query (Mongodb) to sort this collection based on the createdAt with active: true in the package array?
The expectation looks like this:
[
{
student: "c",
package: [
{name: "one", createdAt: "2021-10-10T00:00:00", active: true},
...
]
},
{
student: "a",
package: [
{name: "one", createdAt: "2021-10-12T00:00:00", active: true},
...
]
},
{
student: "b",
package: [
{name: "one", createdAt: "2021-10-16T00:00:00", active: true},
...
]
},
]
Could anyone help me with this? The idea comes up to my mind just to use the code to sort it, but is it possible to use a query MongoDB?

Answer 1

Query
creates a sort-key for each document, this is the latest date of the active package members (the $reduce does, this keeping the max date)
sort by it
unset to remove this extra key
*for descended or ascedent, you can chage the $gt with $lt and the sort 1, with sort -1. depending on what you need. If you use $lt replace "0" also with a max string like "9". Or if you have real dates, with a min or max date.
PlayMongo
aggregate(
[{"$set":
{"sort-key":
{"$reduce":
{"input": "$package",
"initialValue": "0",
"in":
{"$cond":
[{"$and":
["$$this.active", {"$gt": ["$$this.createdAt", "$$value"]}]},
"$$this.createdAt", "$$value"]}}}}},
{"$sort": {"sort-key": 1}},
{"$unset": ["sort-key"]}])

Answer 2

You can use this aggregation query:
First $unwind to deconstruct the array ang get each value.
Then $sort by active.
$group to get the initial data but sorted.
And last $sort again by createdAt.
db.collection.aggregate([
{
"$unwind": "$package"
},
{
"$set": {
"package.createdAt": {
"$toDate": "$package.createdAt"
}
}
},
{
"$sort": {
"package.active": -1
}
},
{
"$group": {
"_id": "$_id",
"student": {
"$first": "$student"
},
"package": {
"$push": "$package"
}
}
},
{
"$sort": {
"package.createdAt": 1
}
}
])
Example here
Also, to do the sorting, is better if createdAt is a Date field, otherwise you should parse to date. Like this example