The has_parent query works the same as the has_parent filter, by automatically wrapping the filter with a constant_score (when using the default score type). It has the same syntax as the has_parent filter.

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

Scoring capabilitiesedit

The has_parent also has scoring support. The supported score types are score or none. The default is none and this ignores the score from the parent document. The score is in this case equal to the boost on the has_parent query (Defaults to 1). If the score type is set to score, then the score of the matching parent document is aggregated into the child documents belonging to the matching parent document. The score type can be specified with the score_mode field inside the has_parent query:

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

Memory Considerationsedit

In order to support parent-child joins, all of the (string) parent IDs must be resident in memory (in the field data cache. Additionally, 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"