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_parent field
edit_parent
field
editA parent-child relationship can be established between documents in the same index by making one mapping type the parent of another:
PUT my_index { "mappings": { "my_parent": {}, "my_child": { "_parent": { "type": "my_parent" } } } } PUT my_index/my_parent/1 { "text": "This is a parent document" } PUT my_index/my_child/2?parent=1 { "text": "This is a child document" } PUT my_index/my_child/3?parent=1 { "text": "This is another child document" } GET my_index/my_parent/_search { "query": { "has_child": { "type": "my_child", "query": { "match": { "text": "child document" } } } } }
The |
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Index a parent document. |
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Index two child documents, specifying the parent document’s ID. |
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Find all parent documents that have children which match the query. |
See the has_child
and
has_parent
queries,
the children
aggregation,
and inner hits for more information.
The value of the _parent
field is accessible in queries, aggregations, scripts,
and when sorting:
GET my_index/_search { "query": { "terms": { "_parent": [ "1" ] } }, "aggs": { "parents": { "terms": { "field": "_parent", "size": 10 } } }, "sort": [ { "_parent": { "order": "desc" } } ], "script_fields": { "parent": { "script": "doc['_parent']" } } }
Querying on the |
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Aggregating on the |
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Sorting on the |
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Accessing the |
Parent-child restrictions
edit- The parent and child types must be different — parent-child relationships cannot be established between documents of the same type.
-
The
_parent.type
setting can only point to a type that doesn’t exist yet. This means that a type cannot become a parent type after it is has been created. -
Parent and child documents must be indexed on the same shard. The
parent
ID is used as the routing value for the child, to ensure that the child is indexed on the same shard as the parent. This means that the sameparent
value needs to be provided when getting, deleting, or updating a child document.
Global ordinals
editParent-child uses global ordinals to speed up joins.
Global ordinals need to be rebuilt after any change to a shard. The more
parent id values are stored in a shard, the longer it takes to rebuild the
global ordinals for the _parent
field.
Global ordinals, by default, are built lazily: the first parent-child query or
aggregation after a refresh will trigger building of global ordinals. This can
introduce a significant latency spike for your users. You can use
eager_global_ordinals to shift the cost of building global
ordinals from query time to refresh time, by mapping the _parent
field as follows:
PUT my_index { "mappings": { "my_parent": {}, "my_child": { "_parent": { "type": "my_parent", "fielddata": { "loading": "eager_global_ordinals" } } } } }
The amount of heap used by global ordinals can be checked as follows:
# Per-index GET _stats/fielddata?human&fields=_parent # Per-node per-index GET _nodes/stats/indices/fielddata?human&fields=_parent