Elasticsearch nested aggregations returns duplicate results [duplicate] - elasticsearch

Question

This question already has an answer here:
how to return the count of unique documents by using elasticsearch aggregation
(1 answer)
Closed 5 years ago.
With this mapping:
PUT pizzas
{
"mappings": {
"pizza": {
"properties": {
"name": {
"type": "keyword"
},
"types": {
"type": "nested",
"properties": {
"topping": {
"type": "keyword"
},
"base": {
"type": "keyword"
}
}
}
}
}
}
}
And this data:
PUT pizzas/pizza/1
{
"name": "meat",
"types": [
{
"topping": "bacon",
"base": "normal"
},
{
"topping": "pepperoni",
"base": "normal"
}
]
}
PUT pizzas/pizza/2
{
"name": "veg",
"types": [
{
"topping": "broccoli",
"base": "normal"
}
]
}
If I run this nested aggregation query:
GET pizzas/_search
{
"size": 0,
"aggs": {
"types_agg": {
"nested": {
"path": "types"
},
"aggs": {
"base_agg": {
"terms": {
"field": "types.base"
}
}
}
}
}
}
I get this result:
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 2,
"max_score": 0,
"hits": []
},
"aggregations": {
"types_agg": {
"doc_count": 3,
"base_agg": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "normal",
"doc_count": 3
}
]
}
}
}
}
I expected my aggregation to return a doc_count of 2 because there are only two documents which match my query. However it is clear that because it's an inverted index, it is finding 3 results and therefore 3 documents.
Is there anyway to get it to return unique document counts?
(tested in Elasticsearch 5.4.3)

Answer 1

Just discovered the answer shortly after asking the question.
Changing the aggregation query to be:
GET pizzas/_search
{
"size": 0,
"aggs": {
"types_agg": {
"nested": {
"path": "types"
},
"aggs": {
"base_agg": {
"terms": {
"field": "types.base"
},
"aggs": {
"top_reverse_nested": {
"reverse_nested": {}
}
}
}
}
}
}
}
Yields the result:
{
"took": 5,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 2,
"max_score": 0,
"hits": []
},
"aggregations": {
"types_agg": {
"doc_count": 3,
"base_agg": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "normal",
"doc_count": 3,
"top_reverse_nested": {
"doc_count": 2
}
}
]
}
}
}
}
The important part which was added to the query was:
"aggs": {
"top_reverse_nested": {
"reverse_nested": {}
}
}
Reverse nested join back to the root of the document so it only gets unique aggregations.
You can read about reverse_nested here.