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WARNING: Version 5.1 of Elasticsearch has passed its EOL date.
This documentation is no longer being maintained and may be removed. If you are running this version, we strongly advise you to upgrade. For the latest information, see the current release documentation.
Inner hits
editInner hits
editThe parent/child and nested features allow the return of documents that have matches in a different scope. In the parent/child case, parent documents are returned based on matches in child documents or child documents are returned based on matches in parent documents. In the nested case, documents are returned based on matches in nested inner objects.
In both cases, the actual matches in the different scopes that caused a document to be returned is hidden. In many cases, it’s very useful to know which inner nested objects (in the case of nested) or children/parent documents (in the case of parent/child) caused certain information to be returned. The inner hits feature can be used for this. This feature returns per search hit in the search response additional nested hits that caused a search hit to match in a different scope.
Inner hits can be used by defining an inner_hits
definition on a nested
, has_child
or has_parent
query and filter.
The structure looks like this:
"<query>" : { "inner_hits" : { <inner_hits_options> } }
If inner_hits
is defined on a query that supports it then each search hit will contain an inner_hits
json object with the following structure:
"hits": [ { "_index": ..., "_type": ..., "_id": ..., "inner_hits": { "<inner_hits_name>": { "hits": { "total": ..., "hits": [ { "_type": ..., "_id": ..., ... }, ... ] } } }, ... }, ... ]
Options
editInner hits support the following options:
|
The offset from where the first hit to fetch for each |
|
The maximum number of hits to return per |
|
How the inner hits should be sorted per |
|
The name to be used for the particular inner hit definition in the response. Useful when multiple inner hits
have been defined in a single search request. The default depends in which query the inner hit is defined.
For |
Inner hits also supports the following per document features:
Nested inner hits
editThe nested inner_hits
can be used to include nested inner objects as inner hits to a search hit.
The example below assumes that there is a nested object field defined with the name comments
:
{ "query" : { "nested" : { "path" : "comments", "query" : { "match" : {"comments.message" : "[actual query]"} }, "inner_hits" : {} } } }
An example of a response snippet that could be generated from the above search request:
... "hits": { ... "hits": [ { "_index": "my-index", "_type": "question", "_id": "1", "_source": ..., "inner_hits": { "comments": { "hits": { "total": ..., "hits": [ { "_nested": { "field": "comments", "offset": 2 }, "_source": ... }, ... ] } } } }, ...
The name used in the inner hit definition in the search request. A custom key can be used via the |
The _nested
metadata is crucial in the above example, because it defines from what inner nested object this inner hit
came from. The field
defines the object array field the nested hit is from and the offset
relative to its location
in the _source
. Due to sorting and scoring the actual location of the hit objects in the inner_hits
is usually
different than the location a nested inner object was defined.
By default the _source
is returned also for the hit objects in inner_hits
, but this can be changed. Either via
_source
filtering feature part of the source can be returned or be disabled. If stored fields are defined on the
nested level these can also be returned via the fields
feature.
An important default is that the _source
returned in hits inside inner_hits
is relative to the _nested
metadata.
So in the above example only the comment part is returned per nested hit and not the entire source of the top level
document that contained the comment.
Hierarchical levels of nested object fields and inner hits.
editIf a mapping has multiple levels of hierarchical nested object fields each level can be accessed via dot notated path.
For example if there is a comments
nested field that contains a votes
nested field and votes should directly be returned
with the root hits then the following path can be defined:
{ "query" : { "nested" : { "path" : "comments.votes", "query" : { ... }, "inner_hits" : {} } } }
This indirect referencing is only supported for nested inner hits.
Parent/child inner hits
editThe parent/child inner_hits
can be used to include parent or child
The examples below assumes that there is a _parent
field mapping in the comment
type:
{ "query" : { "has_child" : { "type" : "comment", "query" : { "match" : {"message" : "[actual query]"} }, "inner_hits" : {} } } }
An example of a response snippet that could be generated from the above search request:
... "hits": { ... "hits": [ { "_index": "my-index", "_type": "question", "_id": "1", "_source": ..., "inner_hits": { "comment": { "hits": { "total": ..., "hits": [ { "_type": "comment", "_id": "5", "_source": ... }, ... ] } } } }, ...
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