136 lines
3.8 KiB
Plaintext
136 lines
3.8 KiB
Plaintext
[[query-dsl-has-child-query]]
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=== Has Child Query
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The `has_child` filter accepts a query and the child type to run against, and
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results in parent documents that have child docs matching the query. Here is
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an example:
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[source,js]
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--------------------------------------------------
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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" : "blog_tag",
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"query" : {
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"term" : {
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"tag" : "something"
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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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// CONSOLE
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Note that the `has_child` is a slow query compared to other queries in the
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query dsl due to the fact that it performs a join. The performance degrades
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as the number of matching child documents pointing to unique parent documents
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increases. If you care about query performance you should not use this query.
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However if you do happen to use this query then use it as little as possible.
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Each `has_child` query that gets added to a search request can increase query
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time significantly.
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[float]
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==== Scoring capabilities
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The `has_child` also has scoring support. The
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supported score modes are `min`, `max`, `sum`, `avg` or `none`. The default is
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`none` and yields the same behaviour as in previous versions. If the
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score mode is set to another value than `none`, the scores of all the
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matching child documents are aggregated into the associated parent
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documents. The score type can be specified with the `score_mode` field
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inside the `has_child` query:
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[source,js]
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--------------------------------------------------
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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" : "blog_tag",
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"score_mode" : "min",
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"query" : {
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"term" : {
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"tag" : "something"
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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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// CONSOLE
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[float]
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[[min-max-children]]
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==== Min/Max Children
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The `has_child` query allows you to specify that a minimum and/or maximum
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number of children are required to match for the parent doc to be considered
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a match:
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[source,js]
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--------------------------------------------------
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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" : "blog_tag",
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"score_mode" : "min",
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"min_children": 2, <1>
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"max_children": 10, <1>
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"query" : {
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"term" : {
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"tag" : "something"
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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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// CONSOLE
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<1> Both `min_children` and `max_children` are optional.
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The `min_children` and `max_children` parameters can be combined with
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the `score_mode` parameter.
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[float]
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==== Ignore Unmapped
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When set to `true` the `ignore_unmapped` option will ignore an unmapped `type`
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and will not match any documents for this query. This can be useful when
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querying multiple indexes which might have different mappings. When set to
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`false` (the default value) the query will throw an exception if the `type`
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is not mapped.
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[float]
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==== Sorting
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Parent documents can't be sorted by fields in matching child documents via the
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regular sort options. If you need to sort parent document by field in the child
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documents then you should use the `function_score` query and then just sort
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by `_score`.
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Sorting blogs by child documents' `click_count` field:
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[source,js]
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--------------------------------------------------
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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" : "blog_tag",
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"score_mode" : "max",
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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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}
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}
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}
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--------------------------------------------------
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// CONSOLE
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