Create Dynamic Alerting Trigger based on Doc's Value inside "_source"

Plugins Alerting
, ,
1

Hi,

My Monitor condition is below.

Monitor- Extraction Query

{
    "size": 1,
    "sort":{"Date":"desc"},
    "query": {
        "bool": {

            "adjust_pure_negative": true,
            "boost": 1
        }
    }
 }

Output-

{
    "_shards": {
        "total": 4,
        "failed": 0,
        "successful": 4,
        "skipped": 0
    },
    "hits": {
        "hits": [
            {
                "_index": "titan_cal_spread",
                "_source": {
                    "symbol": "TITAN",
                    "std_dev": 3.7,
                    "upper_range": 11.1,
                    "current_month_close": 1921.6,
                    "mean": 7.4,
                    "weekday": "Thursday",
                    "difference": 12.050000000000182,
                    "Date": "2022-06-30T00:00:00",
                    "next_month_close": 1933.65,
                    "lower_range": 3.7
                },
                "_id": "A4okuIEB0-WmbmBjPwd4",
                "sort": [
                    1656547200000
                ],
                "_score": null
            }
        ],
        "total": {
            "value": 204,
            "relation": "eq"
        },
        "max_score": null
    },
    "took": 32,
    "timed_out": false
}

I want to create Trigger condition based on fields present inside hits.hits._source to make trigger work on dynamic values present in fields.

Trigger-

return ctx.results[0].hits.hits.params['_source']['difference']  < ctx.results[0].hits.hits.params['_source']['lower_range']

Error-

{
  "type" : "script_exception",
  "reason" : "runtime error",
  "script_stack" : [
    "return ctx.results[0].hits.hits.params['_source']['difference'] < ctx.results[0].hits.hits.params['_source']['lower_range']",
    "                               ^---- HERE"
  ],
  "script" : "return ctx.results[0].hits.hits.params['_source']['difference'] < ctx.results[0].hits.hits.params['_source']['lower_range']",
  "lang" : "painless",
  "position" : {
    "offset" : 31,
    "start" : 0,
    "end" : 123
  },
  "caused_by" : {
    "type" : "illegal_argument_exception",
    "reason" : "Illegal list shortcut value [params]."
  }
}