Elasticsearch search query: why params._source.nested_field.size() is not working in script?

Question

There are lot of questions and answers about this but still didn\'t get a satisfied answers. Elasticsearch version: 6.5

Index mapping

\"_doc\": {
          


        

Answer 1

Despite the fact that this would've been slow and against the guidance of not accessing _source in search queries, the query would have worked before v6.4.

After v6.4, thanks to an unintentional side effect of refactoring, accessing _source in the script query context is not possible.

With that being said, we can "hijack" a function_score query whose Painless context still has access to the _source:

{
  "query": {
    "function_score": {
      "query": {
        "match_all": {}
      },
      "functions": [
        {
          "script_score": {
            "script": {
              "source": "params._source.containsKey('nested_field') && params._source['nested_field'] != null && params._source.nested_field.size() > 1 ? 1 : 0"
            }
          }
        }
      ],
      "min_score": 1
    }
  }
}

---

You could use a pipeline to calculate the field size and then save it on the doc's top level.

Alternatively, you could use copy_to as outlined in my related answer.