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Querying a Nested Object

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Querying a Nested Object

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Because nested objects are indexed as separate hidden documents, we can’t query them directly. Instead, we have to use the nested query to access them:

GET /my_index/blogpost/_search
{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "title": "eggs" 
          }
        },
        {
          "nested": {
            "path": "comments", 
            "query": {
              "bool": {
                "must": [ 
                  {
                    "match": {
                      "comments.name": "john"
                    }
                  },
                  {
                    "match": {
                      "comments.age": 28
                    }
                  }
                ]
              }
            }
          }
        }
      ]
}}}

	The `title` clause operates on the root document.
	The `nested` clause “steps down” into the nested `comments` field. It no longer has access to fields in the root document, nor fields in any other nested document.
	The `comments.name` and `comments.age` clauses operate on the same nested document.

A nested field can contain other nested fields. Similarly, a nested query can contain other nested queries. The nesting hierarchy is applied as you would expect.

Of course, a nested query could match several nested documents. Each matching nested document would have its own relevance score, but these multiple scores need to be reduced to a single score that can be applied to the root document.

By default, it averages the scores of the matching nested documents. This can be controlled by setting the score_mode parameter to avg, max, sum, or even none (in which case the root document gets a constant score of 1.0).

GET /my_index/blogpost/_search
{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "title": "eggs"
          }
        },
        {
          "nested": {
            "path": "comments",
            "score_mode": "max", 
            "query": {
              "bool": {
                "must": [
                  {
                    "match": {
                      "comments.name": "john"
                    }
                  },
                  {
                    "match": {
                      "comments.age": 28
                    }
                  }
                ]
              }
            }
          }
        }
      ]
    }
  }
}

Give the root document the _score from the best-matching nested document.

If placed inside the filter clause of a Boolean query, a nested query behaves much like a nested query, except that it doesn’t accept the score_mode parameter. Because it is being used as a non-scoring query — it includes or excludes, but doesn’t score — a score_mode doesn’t make sense since there is nothing to score.

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