Has child query
editHas child query
editReturns parent documents whose joined child documents match a provided query. You can create parent-child relationships between documents in the same index using a join field mapping.
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.
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.
Example request
editIndex setup
editTo use the has_child
query, your index must include a join
field mapping. For example:
response = client.indices.create( index: 'my-index-000001', body: { mappings: { properties: { "my-join-field": { type: 'join', relations: { parent: 'child' } } } } } ) puts response
PUT /my-index-000001 { "mappings": { "properties": { "my-join-field": { "type": "join", "relations": { "parent": "child" } } } } }
Example query
editGET /_search { "query": { "has_child": { "type": "child", "query": { "match_all": {} }, "max_children": 10, "min_children": 2, "score_mode": "min" } } }
Top-level parameters for has_child
edit-
type
- (Required, string) Name of the child relationship mapped for the join field.
-
query
-
(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. -
ignore_unmapped
-
(Optional, Boolean) Indicates whether to ignore an unmapped
type
and not return any documents instead of an error. Defaults tofalse
.If
false
, Elasticsearch returns an error if thetype
is unmapped.You can use this parameter to query multiple indices that may not contain the
type
. -
max_children
-
(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. -
min_children
-
(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. -
score_mode
-
(Optional, string) Indicates how scores for matching child documents affect the root parent document’s relevance score. Valid values are:
-
none
(Default) -
Do not use the relevance scores of matching child documents. The query assigns
parent documents a score of
0
. -
avg
- Use the mean relevance score of all matching child documents.
-
max
- Uses the highest relevance score of all matching child documents.
-
min
- Uses the lowest relevance score of all matching child documents.
-
sum
- Add together the relevance scores of all matching child documents.
-
Notes
editSorting
editYou cannot sort the results of a has_child
query using standard
sort options.
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.
GET /_search { "query": { "has_child": { "type": "child", "query": { "function_score": { "script_score": { "script": "_score * doc['click_count'].value" } } }, "score_mode": "max" } } }