Get count distinct by nested objects from Elasticsearch - elasticsearch

Question

I have index with following mapping
{
"mappings": {
"properties": {
"typed_obj": {
"type": "nested",
"properties": {
"id": {"type": "keyword"},
"type": {"type": "keyword"}
}
}
}
}
}
and documents
{"index" : {}}
{"typed_obj": [{"id": "1", "type": "one"}, {"id": "2", "type": "two"}]}
{"index" : {}}
{"typed_obj": [{"id": "1", "type": "one"}, {"id": "2", "type": "one"}]}
{"index" : {}}
{"typed_obj": [{"id": "1", "type": "one"}, {"id": "3", "type": "one"}]}
{"index" : {}}
{"typed_obj": [{"id": "1", "type": "one"}, {"id": "4", "type": "two"}]}
How can i group typed_obj by type and calculate unique id ?
Smth like
{
"type": "one",
"count": 3
},
{
"type": "two",
"count": 2
}
I made up query with agg
{
"query": {
"match_all": {}
},
"aggs": {
"obj_nested": {
"nested": {
"path": "typed_obj"
},
"aggs": {
"by_type_and_id": {
"multi_terms": {
"terms": [
{
"field": "typed_obj.type"
},
{
"field": "typed_obj.id"
}
]
}
}
}
}
},
"size": 0
}
and it returns
"buckets": [
{
"key": [
"one",
"1"
],
"key_as_string": "one|1",
"doc_count": 4
},
{
"key": [
"one",
"2"
],
"key_as_string": "one|2",
"doc_count": 1
},
{
"key": [
"one",
"3"
],
"key_as_string": "one|3",
"doc_count": 1
},
{
"key": [
"two",
"2"
],
"key_as_string": "two|2",
"doc_count": 1
},
{
"key": [
"two",
"4"
],
"key_as_string": "two|4",
"doc_count": 1
}
]
In backend app i can group keys by first element (it is typed_obj type) and then retriev length, but my question is - is it possible to get types count without obtain from index all id+type pairs ?

Answer 1

You need to use Cardinality aggregation to count distinct values.
Query:
{
"query": {
"match_all": {}
},
"aggs": {
"obj_nested": {
"nested": {
"path": "typed_obj"
},
"aggs": {
"type":{
"terms": {
"field": "typed_obj.type",
"size": 10
},
"aggs": {
"id": {
"cardinality": {
"field": "typed_obj.id"
}
}
}
}
}
}
},
"size": 0
}
Response
"aggregations" : {
"obj_nested" : {
"doc_count" : 8,
"type" : {
"doc_count_error_upper_bound" : 0,
"sum_other_doc_count" : 0,
"buckets" : [
{
"key" : "one",
"doc_count" : 6,
"id" : {
"value" : 3
}
},
{
"key" : "two",
"doc_count" : 2,
"id" : {
"value" : 2
}
}
]
}
}
}
Note:
A single-value metrics aggregation that calculates an approximate
count of distinct values.