Elasticsearch Nested 2 Step Sorting - sorting

Question

Given the following data with nested objects (members within teams), I need to do a 2 step sort:
Return the youngest member of each team.
Sort the teams by the name of that youngest member.
I have a query below that is close: it does get the youngest member of each team, but then it sorts the teams using the names of all the members, not just the one selected per team.
What would the query be to do this?
And would such a query be performant assuming there was a lot of data? (Probably a few million objects each having 1-3 nested objects.)
Note: Although it's not clear in this simple example, I cannot simply store the youngest member, since in my real world case, the sorting of the nested objects is determined by a formula that includes an external parameter. This is just a very simplified example of the many sorts like this I would have to do on a larger data set, where I need to get the single best matching nested document for each outer document sorted in one way, but then sort the outer objects based on some other property of that selected nested object.
Data
PUT nested_test
{
"mappings": {
"dynamic": "strict",
"properties": {
"team": { "type": "keyword", "index": true, "doc_values": true },
"members": {
"type": "nested",
"properties": {
"name": { "type": "keyword", "index": true, "doc_values": true },
"age": { "type": "integer", "index": true, "doc_values": true}
}
}
}
}
}
PUT nested_test/_doc/1
{
"team" : "A" ,
"members" :
[
{ "name" : "Curt" , "age" : "34" } ,
{ "name" : "Dave" , "age" : "33" }
]
}
PUT nested_test/_doc/2
{
"team" : "B" ,
"members" :
[
{ "name" : "Alex" , "age" : "36" } ,
{ "name" : "Earl" , "age" : "32" }
]
}
PUT nested_test/_doc/3
{
"team" : "C" ,
"members" :
[
{ "name" : "Brad" , "age" : "35" } ,
{ "name" : "Gary" , "age" : "31" }
]
}
Attempted Query
GET nested_test/_search?filter_path=hits.hits._source.team,hits.hits.sort.*,hits.hits.inner_hits.members.hits.hits._source.*,hits.hits.inner_hits.members.hits.hits.sort.*
{
"query": {
"bool": {
"filter": [
{
"nested": {
"path": "members",
"query": {
"match_all" : { }
} ,
"inner_hits": {
"size": 1,
"sort": {
"members.age": { "order": "asc" }
}
}
}
}
]
}
}
,
"sort": [
{ "members.name": {
"order": "asc" ,
"nested": {
"path": "members",
"filter": { "match_all" : { } }
}
} }
]
}
Results (If the query was correct, the teams would be in A, B, C order, but they are B, C, A)
{
"hits" : {
"hits" : [
{
"_source" : {
"team" : "B"
},
"inner_hits" : {
"members" : {
"hits" : {
"hits" : [
{
"_source" : {
"name" : "Earl",
"age" : "32"
}
}
]
}
}
}
},
{
"_source" : {
"team" : "C"
},
"inner_hits" : {
"members" : {
"hits" : {
"hits" : [
{
"_source" : {
"name" : "Gary",
"age" : "31"
}
}
]
}
}
}
},
{
"_source" : {
"team" : "A"
},
"inner_hits" : {
"members" : {
"hits" : {
"hits" : [
{
"_source" : {
"name" : "Dave",
"age" : "33"
}
}
]
}
}
}
}
]
}
}

Answer 1

I not feasable with nested sort. And you cant use the result of the inner_hits to sort your documents.
You could maybe use some runtime field with a complex script to extract the name of the youngest member at search time, but it will certainly be ugly and the performance of the query will be impacted, it will perform poorly at scale.
Since you use a nested model, you have all the data needed during indexation to store the youngest member name in a specific field at the root of the document.
Then you will be able to use a standard sort for this use case.
Its the right way to do it in Elasticsearch it you want to keep the performance.