Bucket sort on dynamic aggregation name - elasticsearch

Question

I would like to sort my aggregations value from quantity.
But my problem is that each aggregation have a name that couldn't be know in advance :
Given this query :
{
"size": 0,
"query": {
"bool": {
"must": [
{
"range": {
"datetime": {
"gte": "2021-01-01",
"lte": "2021-12-09"
}
}
}
]
}
},
"aggs": {
"sorting": {
"bucket_sort": {
"sort": [
{
"year>quantity": {
"order": "desc"
}
}
]
}
},
"UNKNOWN_1": {
"aggs": {
"year": {
"filter": {
"bool": {
"must": [
{
"range": {
"datetime": {
"gte": "2021-01-01",
"lte": "2021-12-09"
}
}
}
]
}
},
"aggs": {
"quantity": {
"sum": {
"field": "item.quantity"
}
}
}
}
}
},
"UNKNOWN_2": {
"aggs": {
"year": {
"aggs": {
"quantity": {
"sum": {
"field": "item.quantity"
}
}
}
}
}
},
....
}
}
it miss one level on my bucket_sort aggregation to reach that quantity value.
Here is one elastic record :
{
datetime: '2021-12-01',
item.quantity: 5
}
Note that I have remove the biggest part of the request for comprehension, like filter aggregation, ect....
I tried something with wildcard :
"sorting": {
"bucket_sort": {
"sort": [
{
"*>year>quantity": {
"order": "desc"
}
}
]
}
},
But got the same error....
Is it possible to achieve this behaviour ?

Answer 1

I think you misunderstood the "bucket_sort" aggregation: it won't sort your aggregations but it sorts the buckets coming from one multi-bucket aggregation. Also the bucket_sort aggregation has to be subordinate to that multi-bucket aggregation.
From the docs:
[The bucket sort aggregation is] "a parent pipeline aggregation which sorts the buckets of its parent multi-bucket aggregation"
If I get it correct, you try to create "buckets" with specific filter aggregations and you can't know in advance how many of those filter aggregations you create.
For that you can use the "multi filters" aggregation where you can specify as many filters as you want and each of them creates a bucket.
Subordinated to that filters-aggregation you can create one single sum aggregation on item.quantity.
Also subordinated to the filters-aggregations you then add your buckets_sort aggregation, where you also just have to name the sibling "sum" aggregation.
All in all it might look like that:
{
"aggs": {
"your_filters": {
"filters": {
"filters": {
"unknown_1": {
"range": {
"datetime": {
"gte": "2021-01-01",
"lte": "2021-12-09"
}
}
},
"unknown_2": {
/** more filters here... **/
}
}
},
"aggs": {
"quantity": {
"sum": {
"field": "item.quantity"
}
},
"sorting": {
"bucket_sort": {
"sort": [
{ "quantity": { "order": "desc" } }
]
}
}
}
}
}
}