Merge the results of two aggregations

Question

I have an Elasticsearch index with documents that have the following fields:

• author
• contributor

Each of these fields may contain multiple user IDs.

I want to perform an aggregation that counts the total number of documents related to each user (either as author or contributor).

I can query each aggregation separately, but how do I combine them? Here's my query:

GET documents/_search
{
  "aggs": {
    "contributor": {
      "terms": {
        "field": "contributor"
      }
    },
    "author": {
      "terms": {
        "field": "author"
      }
    }
  }
}

Right now, I'm getting this result:

"aggregations": {
    "author": {
        "doc_count_error_upper_bound": 0,
        "sum_other_doc_count": 0,
        "buckets": [{
                "key": 2,
                "doc_count": 10
            },
            {
                "key": 1,
                "doc_count": 7
            },
            {
                "key": 5,
                "doc_count": 3
            }
        ]
    },
    "contributor": {
        "doc_count_error_upper_bound": 0,
        "sum_other_doc_count": 0,
        "buckets": [{
            "key": 5,
            "doc_count": 1
        }]
    }
}

But I'd like to have a single aggregation that returns the count of 4 documents for user 5.

Answer 1

Well if you can update your mappings and add a field this should work. Please not it could be really slow (agg on string are slow and shouldnot be over used). Note if author = contributor in the same doc the agg will wont count 2 occurance (good news).

    {
      "mappings": {
        "test": {
          "properties": {
            "contributor": {
              "type": "keyword",
              "copy_to": "author_and_contributor"
            },
            "author": {
              "type": "keyword",
              "copy_to": "author_and_contributor"
            },
            "author_and_contributor": {
              "type": "string",
              "fielddata": true
            }
          }
        }
      }
}

{
  "size": 0,
  "aggs": {
    "author_contrib_agg": {
      "terms": {
        "field": "author_and_contributor"
      }
    }
  }
}