Access array in script_score

Question

For one of my ElasticSearch queries, I'd like to define define a function score and sort by it. The function score takes the computed score and adds a boost value to it. Each document has its boost value stored in a numeric field.

Like this:

{
    "from": 0,
    "size": 10,
    "query": {
        "function_score": {
            "functions": [
                {
                    "script_score": {
                        "script": "_score + doc['boostFactor'].value"
                    }
                }
            ],
            "query": {
                "filtered": {
                    "query": {
                        "query_string": {
                            "query": "search for this!"
                        }
                    }
                }
            },
            "boost_mode": "replace"
        }
    }
}

So far so good, this works fine. Now here's the problem: going forward, each document will have an array of boost values:

"boostFactor": [ 0, 0.5, 1, 3 ]

When firing up the query, I'd like the script score to pick a particular element of the array, based on a predefined index. So let's say index=2, then the script score would potentially look like this:

                "script_score": {
                    "script": "_score + doc['boostFactor'][2].value"
                }

Unfortunately, ElasticSearch doesn't accept this:

...Query Failed [Failed to execute main query]]; 
nested: CompileException[[Error: unexpected token in constructor]...

Any ideas?

Answer 1

doc['boostFactor'].value returns a single value. To get the whole array, use doc['boostFactor'].values; then you can get a specific index within the array as you'd expect:

            {
                "script_score": {
                    "script": "_score + doc['boostFactor'].values[2]"
                }
            }

See the scripting section of the Elasticsearch docs for more info: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-scripting.html