The has_child query and filter can be used to find parent documents based on the contents of their children. For instance, we could find all branches that have employees born after 1980 with a query like this:

GET /company/branch/_search
{
  "query": {
    "has_child": {
      "type": "employee",
      "query": {
        "range": {
          "dob": {
            "gte": "1980-01-01"
          }
        }
      }
    }
  }
}

Like the nested query, the has_child query could match several child documents, each with a different relevance score. How these scores are reduced to a single score for the parent document depends on the score_mode parameter. The default setting is none, which ignores the child scores and assigns a score of 1.0 to the parents, but it also accepts avg, min, max, and sum.

The following query will return both london and liverpool, but london will get a better score because Alice Smith is a better match than Barry Smith:

GET /company/branch/_search
{
  "query": {
    "has_child": {
      "type":       "employee",
      "score_mode": "max",
      "query": {
        "match": {
          "name": "Alice Smith"
        }
      }
    }
  }
}

The default score_mode of none is significantly faster than the other modes because Elasticsearch doesn’t need to calculate the score for each child document. Set it to avg, min, max, or sum only if you care about the score.

GET /company/branch/_search
{
  "query": {
    "has_child": {
      "type":         "employee",
      "min_children": 2, 
      "query": {
        "match_all": {}
      }
    }
  }
}