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"
            }
        }
    }
}

Scoring capabilitiesedit

The has_child also has scoring support. The supported score types are min, max, sum, avg or none. The default is none and yields the same behaviour as in previous versions. If the score type is set to another value than none, the scores of all the matching child documents are aggregated into the associated parent documents. The score type can be specified with the score_mode field inside the has_child query:

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

Min/Max Childrenedit

The has_child query allows you to specify that a minimum and/or maximum number of children are required to match for the parent doc to be considered a match:

{
    "has_child" : {
        "type" : "blog_tag",
        "score_mode" : "sum",
        "min_children": 2, 
        "max_children": 10, 
        "query" : {
            "term" : {
                "tag" : "something"
            }
        }
    }
}

The min_children and max_children parameters can be combined with the score_mode parameter.