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