How can I retrieve matching children only?

Question

Consider a very simple model where we have locations and each location can have zero or more events. A location would have properties such as name, description and geo point data (lon/lat). An event should be attached to one location (its parent) and should have a name and description.

{
    "location" : {
        "properties": {
            "name": { "type": "string", "boost": 2.0, "analyzer": "snowball" },
            "description": { "type": "string", "analyzer": "snowball" },
            "geo": { "type": "geo_point" },
            "exhibits": {
                "type": "nested",
                "properties": {
                    "name": { "type": "string", "boost": 2.0, "analyzer": "snowball" },
                    "description": { "type": "string", "analyzer": "snowball" }
                }
            }
        }
    }
}

What I want to be able to do, is to query for the child documents (events) performing a full text search on their names and descriptions. I would like to get the matching events back and be able to also get their parent location's name. I would also like to narrow down the result set by location's coordinates. I don't want to get any events that do not match the query. Is that possible in Elastic Search? What types of queries should I use?

I have tried putting events as an array property under location (see above) and using the nested query but it does not return the kind of results I want (I think it returns the whole location, including all events, even the ones that do not match my query). I have tried putting events into a separate index (mapping?) providing the _parent property and then performing the top_children query on locations, but I don't get any results.

{
    "exhibit": {
        "_parent": { "type": "locations" },
        "properties": {
            "name": { "type": "string", "boost": 2.0, "analyzer": "snowball" },
            "description": { "type": "string", "analyzer": "snowball" }
        }
    }
}

Could anyone shed some light? I don't know where to begin...

Answer 1

Here's the working solution to my problem, perhaps it will be useful to somebody.

Location mapping:

{
    "location" : {
        "properties": {
            "name": { "type": "string", "boost": 2.0, "analyzer": "snowball" },
            "description": { "type": "string", "analyzer": "snowball" },
            "geo": { "type": "geo_point" }
        }
    }
}

Exhibit mapping:

{
    "exhibit": {
        "_parent": { "type": "locations" },
        "properties": {
            "name": { "type": "string", "boost": 2.0, "analyzer": "snowball" },
            "description": { "type": "string", "analyzer": "snowball" }
        }
    }
}

Query:

{
    "fields": [ "_parent", "name", "_source" ],
    "query": {
        "bool": {
            "should": [ 
                { "text": { "name": "candy" } },
                { "text": { "description": "candy" } } 
            ]
        }
    },
    "filter": { 
        "and": [
            {
                "terms" : {
                    "_parent": [ "4e7089a9b97d640b30695b7a", "4e7089eeb97d640b30695b7b" ]
                }
            },
            { "range": { "start": { "lte": "2011-09-22" } } },
            { "range": { "end": { "gte": "2011-09-22" } } }
        ]
    }
}

You should query using the _parent field and passing it an array of IDs of locations to which you want to limit the exhibits.