135 lines
4.2 KiB
Markdown
135 lines
4.2 KiB
Markdown
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---
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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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