Elasticsearch：按数组中的最大值排序

Question

Let's say I have 2 documents:

{
  "id": "1234",
  "things": [
    {
      "datetime": "2016-01-01T12:00:00+03:00"
    },
    {
      "datetime": "2016-01-06T12:00:00+03:00"
    },
    {
      "datetime": "2100-01-01T12:00:00+03:00"
    }
  ]
}

and

{
  "id": "5678",
  "things": [
    {
      "datetime": "2016-01-03T12:00:00+03:00"
    },
    {
      "datetime": "2100-01-06T12:00:00+03:00"
    }
  ]
}

things.datetime is mapped as { "type": "date", "format": "date_time_no_millis" }.

I want to sort these documents based on the latest things.datetime value that is not in the future.

Ie sorted by simply the max things.datetime would use the dates 2100-01-01T12:00:00+03:00 and 2100-01-06T12:00:00+03:00. I want the sorting to be based on the values 2016-01-06T12:00:00+03:00 and 2016-01-03T12:00:00+03:00.

How can I achieve this, using ElasticSearch 2.x?

I've tried:

"sort": {
  "things.datetime": {
    "order": "desc", 
    "mode": "max"
  }
}

But that doesn't seem to sort even by the 2100 dates.

I also tried to use nested_filter like so:

"sort": {
  "things.datetime": {
    "order": "desc", 
    "mode": "max",
    "nested_filter": {
      "range": {
        "things.datetime": { "lte": "now" }
      }
    }
  }
}

But it doesn't work as I'd expect.

Also the "sort" value in the response is a negative number. So for a document with dates:

"2015-10-24T05:50:00+03:00",
"2015-10-26T22:05:48+02:00",
"2015-10-24T08:05:43+03:00"

gets a negative sort value:

"sort": [
  -9223372036854775808
]

Answer 1

The correct way to achieve this seems to be:

"sort": {
  "things.datetime": {
    "order": "desc", 
    "mode": "max",
    "nested_path": "things",
    "nested_filter": {
      "range": {
        "things.datetime": { "lte": "now" }
      }
    }
  }
}

When there are no more dates left after the nested_filter, the sort value becomes a negative number to ensure the correct order.