Has Parent Filter

The has_parent filter accepts a query and a parent type. The query is executed in the parent document space, which is specified by the parent type. This filter returns child documents which associated parents have matched. For the rest has_parent filter has the same options and works in the same manner as the has_child filter.

Filter example

{
    "has_parent" : {
        "parent_type" : "blog",
        "query" : {
            "term" : {
                "tag" : "something"
            }
        }
    }
}

The parent_type field name can also be abbreviated to type.

The way that the filter is implemented is by first running the parent query, doing the matching up to the child doc for each document matched.

The has_parent filter also accepts a filter instead of a query:

{
    "has_parent" : {
        "type" : "blog",
        "filter" : {
            "term" : {
                "text" : "bonsai three"
            }
        }
    }
}

Memory Considerations

In order to support parent-child joins, all of the (string) parent IDs must be resident in memory (in the field data cache. Additionaly, every child document is mapped to its parent using a long value (approximately). It is advisable to keep the string parent ID short in order to reduce memory usage.

You can check how much memory is being used by the ID cache using the indices stats or nodes stats APIS, eg:

curl -XGET "http://localhost:9200/_stats/id_cache?pretty&human"

Caching

The has_parent filter cannot be cached in the filter cache. The _cache and _cache_key options are a no-op in this filter. Also any filter that wraps the has_parent filter either directly or indirectly will not be cached.