How can I get ElasticSearch aggregations to count the parent documents instead of the nested documents

Question

My ElasticSearch index has nested documents to indicate the places where various events occurred related to the document. I am using aggregations to get facets of the places. The count returned is the count of the number of occurrences of the place. For example, if a document has a birth and death place of California, the aggregation count for California is 2. I would like the aggregation count to be the number of documents containing a particular place, rather than the number of child documents containing the place. The relevant part of my schema looks like this:

"mappings": {
    "document": {
        "properties": {
            "docId" : { "type": "keyword" },
            "place": {
                "type": "nested",
                "properties": {
                    "id": { "type": "keyword" },
                    "type": { "type": "keyword" },
                    "loc": { "type" : "geo_point" },
                    "text": { 
                        "type": "text",
                        "analyzer": "english",
                        "copy_to" : "text"
                    }
                },
                "dynamic": false
            }
        }
    }
}

I can get facets with a simple aggregation like this, which retrieves the places with type place.vital.* (e.g. place.vital.birth, place.vital.death, etc), but counts the number of nested documents, not the number of parent documents.

"aggs": {
"place.vital": {
  "aggs": {
    "types": {
      "aggs": {
        "values": {
          "terms": {
            "field": "place.id"
          }
        }
      },
      "terms": {
        "field": "place.type",
        "include": "place\\.vital\\..*"
      }
    }
  },
  "nested": {
    "path": "place"
  }
}

Is it possible to tweak my aggregation so that it only counts each parent document once?

richardwhatever richardwhatever · Accepted Answer · 2018-02-14T22:42:28

Use reverse nested aggregation. This will then create an aggregation with the nested counts and a sub aggregation with the parent counts.

See how to return the count of unique documents by using elasticsearch aggregation for more detail.

How can I get ElasticSearch aggregations to count the parent documents instead of the nested documents

2 Answers