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Has child

发布于 2019-07-04 字数 3517 浏览 851 评论 0

[[has-child]]
=== Finding Parents by Their Children

The has_child query and filter can be used to find parent documents based on
the contents of their children.(((“has_child query and filter”)))(((“parent-child relationship”, “finding parents by their children”))) For instance, we could find all branches that
have employees born after 1980 with a query like this:

[source,json]

GET /company/branch/_search { “query”: { “has_child”: { “type”: “employee”, “query”: { “range”: { “dob”: { “gte”: “1980-01-01” } } } } } }

Like the <<nested-query,nested query>>, the has_child query could
match several child documents,(((“has_child query and filter”, “query”))) each with a different relevance
score. How these scores are reduced to a single score for the parent document
depends on the score_mode parameter. The default setting is none, which
ignores the child scores and assigns a score of 1.0 to the parents, but it
also accepts avg, min, max, and sum.

The following query will return both london and liverpool, but london
will get a better score because Alice Smith is a better match than
Barry Smith:

[source,json]

GET /company/branch/_search { “query”: { “has_child”: { “type”: “employee”, “score_mode”: “max”, “query”: { “match”: { “name”: “Alice Smith” } } } } }

TIP: The default score_mode of none is significantly faster than the other
modes because Elasticsearch doesn’t need to calculate the score for each child
document. Set it to avg, min, max, or sum only if you care about the
score.(((“parent-child relationship”, “finding parents by their children”, “min_children and max_children”)))

[[min-max-children]]
==== min_children and max_children

The has_child query and filter both accept the min_children and
max_children parameters,(((“min_children parameter”)))(((“max_children parameter”)))(((“has_child query and filter”, “min_children or max_children parameters”))) which will return the parent document only if the
number of matching children is within the specified range.

This query will match only branches that have at least two employees:

[source,json]

GET /company/branch/_search { “query”: { “has_child”: { “type”: “employee”, “min_children”: 2, “query”: { “match_all”: {} } } } }

A branch must have at least two employees in order to match.

The performance of a has_child query or filter with the min_children or
max_children parameters is much the same as a has_child query with scoring
enabled.

.has_child Filter


The has_child filter works(((“has_child query and filter”, “filter”))) in the same way as the has_child query, except
that it doesn’t support the score_mode parameter. It can be used only in
filter context—such as inside a filtered query–and behaves
like any other filter: it includes or excludes, but doesn’t score.

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


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