[[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, <1> "query": { "match_all": {} } } } } ------------------------- <1> 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_&#x2014;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. **************************