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Elasticsearch: The Definitive Guide [2.x] » Modeling Your Data » Parent-Child Relationship » Children Aggregation
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Children Aggregationedit

Parent-child supports a children aggregation as a direct analog to the nested aggregation discussed in Nested Aggregations. A parent aggregation (the equivalent of reverse_nested) is not supported.

This example demonstrates how we could determine the favorite hobbies of our employees by country:

GET /company/branch/_search
{
  "size" : 0,
  "aggs": {
    "country": {
      "terms": { 
        "field": "country"
      },
      "aggs": {
        "employees": {
          "children": { 
            "type": "employee"
          },
          "aggs": {
            "hobby": {
              "terms": { 
                "field": "hobby"
              }
            }
          }
        }
      }
    }
  }
}

The country field in the branch documents.

The children aggregation joins the parent documents with their associated children of type employee.

The hobby field from the employee child documents.
« Finding Children by Their Parents Grandparents and Grandchildren »