While a nested query can always return only the root document as a result, parent and child documents are independent and each can be queried independently. The has_child query allows us to return parents based on data in their children, and the has_parent query returns children based on data in their parents.

It looks very similar to the has_child query. This example returns employees who work in the UK:

GET /company/employee/_search
{
  "query": {
    "has_parent": {
      "type": "branch", 
      "query": {
        "match": {
          "country": "UK"
        }
      }
    }
  }
}

The has_parent query also supports the score_mode, but it accepts only two settings: none (the default) and score. Each child can have only one parent, so there is no need to reduce multiple scores into a single score for the child. The choice is simply between using the score (score) or not (none).