Has Child Query
editHas Child Query
editThe 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:
GET /_search { "query": { "has_child" : { "type" : "blog_tag", "query" : { "term" : { "tag" : "something" } } } } }
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 little as possible.
Each has_child
query that gets added to a search request can increase query
time significantly.
Scoring capabilities
editThe 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:
GET /_search { "query": { "has_child" : { "type" : "blog_tag", "score_mode" : "min", "query" : { "term" : { "tag" : "something" } } } } }
Min/Max Children
editThe 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:
GET /_search { "query": { "has_child" : { "type" : "blog_tag", "score_mode" : "min", "min_children": 2, "max_children": 10, "query" : { "term" : { "tag" : "something" } } } } }
The min_children
and max_children
parameters can be combined with
the score_mode
parameter.
Ignore Unmapped
editWhen 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.
Sorting
editParent 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:
GET /_search { "query": { "has_child" : { "type" : "blog_tag", "score_mode" : "max", "query" : { "function_score" : { "script_score": { "script": "_score * doc['click_count'].value" } } } } } }