Sort Aggregated Buckets From Nested Object Array By Specific Field - elasticsearch

Question

I have indexed documents such as
// doc 1
{
...,
"list": [{
"value": "a",
"order": 1
}, {
"value": "b",
"order": 2
}]
,...
}
// doc 2
{
...,
"list": [{
"value": "b",
"order": 2
}, {
"value": "c",
"order": 3
}]
,...
}
If I use the aggregation on the list.value:
{
"aggs": {
"values": {
"terms": {
"field": "list.value.keyword"
}
}
}
}
I get buckets in order b, a, c:
"buckets" : [
{
"key" : "b",
"doc_count" : 2
},
{
"key" : "a",
"doc_count" : 1
},
{
"key" : "c",
"doc_count" : 1
}
]
as keys would be sorted by the _count in desc order.
If I use the aggregation on the list.value with sub-aggregation for sorting in form of max(list.order):
{
"aggs": {
"values": {
"terms": {
"field": "list.value.keyword",
"order": { "max_order": "desc" }
},
"aggs": {
"max_order": { "max": { "field": "list.order" } }
}
}
}
}
I get buckets in order b, c, a
"buckets" : [
{
"key" : "b",
"doc_count" : 2,
"max_order" : {
"value" : 3.0
}
},
{
"key" : "c",
"doc_count" : 1,
"max_order" : {
"value" : 3.0
}
},
{
"key" : "a",
"doc_count" : 1,
"max_order" : {
"value" : 2.0
}
}
]
as both b and c have max order 3 in their lists of the object.
However, I want to write a query to get buckets in order c, b, a as their order is 3, 2, 1 respectively. How to achieve that?

Answer 1

You need to use nested aggregation, to get the buckets in order of c,b,a
Adding a working example with index data, mapping, search query and search result
Index Mapping
PUT testidx1
{
"mappings":{
"properties": {
"list":{
"type": "nested"
}
}
}
}
Index Data:
POST testidx1/_doc/1
{
"list": [
{
"value": "a",
"order": 1
},
{
"value": "b",
"order": 2
}
]
}
POST testidx1/_doc/2
{
"list": [
{
"value": "b",
"order": 2
},
{
"value": "c",
"order": 3
}
]
}
Search Query:
POST testidx1/_search
{
"size": 0,
"aggs": {
"resellers": {
"nested": {
"path": "list"
},
"aggs": {
"unique_values": {
"terms": {
"field": "list.value.keyword",
"order": {
"max_order": "desc"
}
},
"aggs": {
"max_order": {
"max": {
"field": "list.order"
}
}
}
}
}
}
}
}
Search Response:
"aggregations" : {
"resellers" : {
"doc_count" : 4,
"unique_values" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : "c",
"doc_count" : 1,
"max_order" : {
"value" : 3.0
}
},
{
"key" : "b",
"doc_count" : 2,
"max_order" : {
"value" : 2.0
}
},
{
"key" : "a",
"doc_count" : 1,
"max_order" : {
"value" : 1.0
}
}
]
}
}
}
}