cannot convert MethodHandle(Dates)JodaCompatibleZonedDateTime to (Object)double

Question

I am trying to add conditions if field exist, then sort according to it otherwise use another field. Since one of either will exist. Here is my query:

GET /my_index/_search
{
  "query": {
    "match_all": {}
  },
  "sort": {
    "_script": {
      "type":"number",
      "script": "if(doc['contextDates.event.date'].value != 0){ return doc['contextDates.event.date'].value} else { return doc['contextDates.start.date'].value}",
    "order": "asc"
    }
  }
}

When I execute this query, I get following error:

"failed_shards" : [
      {
        "shard" : 0,
        "index" : "my_inedx",
        "node" : "UxKwS8SIR-uIbzo5_0IbcQ",
        "reason" : {
          "type" : "script_exception",
          "reason" : "runtime error",
          "script_stack" : [
            "return doc['contextDates.event.date'].value} else { ",
            "                                     ^---- HERE"
          ],
          "script" : "if(doc['contextDates.event.date'].value != 0){ return doc['contextDates.event.date'].value} else { return doc['contextDates.start.date'].value}",
          "lang" : "painless",
          "position" : {
            "offset" : 84,
            "start" : 47,
            "end" : 99
          },
          "caused_by" : {
            "type" : "wrong_method_type_exception",
            "reason" : "cannot convert MethodHandle(Dates)JodaCompatibleZonedDateTime to (Object)double"
          }
        }
      }
    ]

I have tried Double.parseDouble method as well but it doesn't work. This is what I have inside document for contextDates

"contextDates" : {
        "event" : {
         "date" : "2020-06-26T00:00:00.000Z",
         "resolution" : "day",
         "score" : 0,
         "type" : "event"
       }
     }

Answer 1

The doc value you're getting is of type JodaCompatibleZonedDateTime which you're trying to compare to a double value, so you need to modify your script like this

if(doc['contextDates.event.date'].value.getMillis() != 0){ return doc['contextDates.event.date'].value.getMillis()} else { return doc['contextDates.start.date'].value.getMillis()}