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In a few previous PR's we restructured the ES|QL docs to make it possible to generate them dynamically. This PR just moves a few files around to make the query languages docs easier to work with, and a little more organized like the ES|QL docs. A bit part of this was setting up redirects to the new locations, so other repo's could correctly link to the elasticsearch docs.
134 lines
4.2 KiB
Markdown
134 lines
4.2 KiB
Markdown
---
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navigation_title: "Has child"
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mapped_pages:
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- https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-has-child-query.html
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---
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# Has child query [query-dsl-has-child-query]
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Returns parent documents whose [joined](/reference/elasticsearch/mapping-reference/parent-join.md) child documents match a provided query. You can create parent-child relationships between documents in the same index using a [join](/reference/elasticsearch/mapping-reference/parent-join.md) field mapping.
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::::{warning}
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Because it performs a join, the `has_child` is slow compared to other queries. Its performance degrades as the number of matching child documents pointing to unique parent documents increases. Each `has_child` query in a search can increase query time significantly.
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If you care about query performance, do not use this query. If you need to use the `has_child` query, use it as rarely as possible.
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::::
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## Example request [has-child-query-ex-request]
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### Index setup [has-child-index-setup]
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To use the `has_child` query, your index must include a [join](/reference/elasticsearch/mapping-reference/parent-join.md) field mapping. For example:
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```console
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PUT /my-index-000001
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{
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"mappings": {
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"properties": {
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"my-join-field": {
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"type": "join",
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"relations": {
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"parent": "child"
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}
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}
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}
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}
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}
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```
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### Example query [has-child-query-ex-query]
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```console
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GET /_search
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{
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"query": {
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"has_child": {
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"type": "child",
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"query": {
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"match_all": {}
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},
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"max_children": 10,
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"min_children": 2,
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"score_mode": "min"
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}
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}
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}
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```
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## Top-level parameters for `has_child` [has-child-top-level-params]
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`type`
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: (Required, string) Name of the child relationship mapped for the [join](/reference/elasticsearch/mapping-reference/parent-join.md) field.
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`query`
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: (Required, query object) Query you wish to run on child documents of the `type` field. If a child document matches the search, the query returns the parent document.
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`ignore_unmapped`
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: (Optional, Boolean) Indicates whether to ignore an unmapped `type` and not return any documents instead of an error. Defaults to `false`.
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If `false`, {{es}} returns an error if the `type` is unmapped.
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You can use this parameter to query multiple indices that may not contain the `type`.
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`max_children`
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: (Optional, integer) Maximum number of child documents that match the `query` allowed for a returned parent document. If the parent document exceeds this limit, it is excluded from the search results.
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`min_children`
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: (Optional, integer) Minimum number of child documents that match the `query` required to match the query for a returned parent document. If the parent document does not meet this limit, it is excluded from the search results.
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`score_mode`
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: (Optional, string) Indicates how scores for matching child documents affect the root parent document’s [relevance score](/reference/query-languages/query-dsl/query-filter-context.md#relevance-scores). Valid values are:
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`none` (Default)
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: Do not use the relevance scores of matching child documents. The query assigns parent documents a score of `0`.
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`avg`
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: Use the mean relevance score of all matching child documents.
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`max`
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: Uses the highest relevance score of all matching child documents.
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`min`
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: Uses the lowest relevance score of all matching child documents.
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`sum`
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: Add together the relevance scores of all matching child documents.
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## Notes [has-child-query-notes]
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### Sorting [has-child-query-performance]
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You cannot sort the results of a `has_child` query using standard [sort options](/reference/elasticsearch/rest-apis/sort-search-results.md).
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If you need to sort returned documents by a field in their child documents, use a `function_score` query and sort by `_score`. For example, the following query sorts returned documents by the `click_count` field of their child documents.
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```console
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GET /_search
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{
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"query": {
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"has_child": {
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"type": "child",
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"query": {
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"function_score": {
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"script_score": {
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"script": "_score * doc['click_count'].value"
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}
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}
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},
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"score_mode": "max"
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}
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}
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}
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```
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