Has Child Filter

The has_child filter accepts a query and the child type to run against, and results in parent documents that have child docs matching the query. Here is an example:

{
    "has_child" : {
        "type" : "blog_tag",
        "query" : {
            "term" : {
                "tag" : "something"
            }
        }
    }
}

The type is the child type to query against. The parent type to return is automatically detected based on the mappings.

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

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

{
    "has_child" : {
        "type" : "comment",
        "filter" : {
            "term" : {
                "user" : "john"
            }
        }
    }
}

With the current implementation, all _id values are loaded to memory (heap) in order to support fast lookups, so make sure there is enough memory for it.

The has_child 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_child filter either directly or indirectly will not be cached.