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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.

A nested filter behaves much like a nested query, except that it doesn’t accept the score_mode parameter. It can be used only in filter context—such as inside a filtered query—and it behaves like any other filter: it includes or excludes, but it doesn’t score.

While the results of the nested filter itself are not cached, the usual caching rules apply to the filter inside the nested filter.

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