Formatting of dates returned by query

[markpavey]

The Elasticsearch documentation about the date data type says:

Multiple formats can be specified by separating them with || as a separator. Each format will be tried in turn until a matching format is found. The first format will be used to convert the milliseconds-since-the-epoch value back into a string.

https://www.elastic.co/guide/en/elasticsearch/reference/current/date.html#multiple-date-formats

If I do the following:

PUT date_mapping_test
{
  "mappings": {
    "date_test": {
      "properties": {
        "date": {
          "type": "date",
          "format": "yyyy-MM-dd HH:mm:ss||yyyy-MM-dd||epoch_millis"
        }
      }
    }
  }
}

PUT date_mapping_test/date_test/1
{
  "date": 1507804756000
}

PUT date_mapping_test/date_test/2
{
  "date": "2017-10-11"
}

PUT date_mapping_test/date_test/3
{
  "date": "2017-10-11 11:41:00"
}

GET date_mapping_test/date_test/_mapping

GET date_mapping_test/date_test/_search

Then I get the following response showing the date field values in the format that they were indexed.

  "hits": {
    "total": 3,
    "max_score": 1,
    "hits": [
      {
        "_index": "date_mapping_test",
        "_type": "date_test",
        "_id": "2",
        "_score": 1,
        "_source": {
          "date": "2017-10-11"
        }
      },
      {
        "_index": "date_mapping_test",
        "_type": "date_test",
        "_id": "1",
        "_score": 1,
        "_source": {
          "date": 1507804756000
        }
      },
      {
        "_index": "date_mapping_test",
        "_type": "date_test",
        "_id": "3",
        "_score": 1,
        "_source": {
          "date": "2017-10-11 11:41:00"
        }
      }
    ]
  }

Whereas the documentation quoted above implies the dates should be formatted according to the first format in the list in the mapping, i.e. "yyyy-MM-dd HH:mm:ss".

Am I doing something wrong or misunderstanding the documentation, or is this a bug?

I am using Elasticsearch 5.5.1 on Windows.

[dadoonet (David Pilato)]

May it's unclear.

Elasticsearch never modifies the JSON document you sent. It's stored in _source field as is.

But if you store specifically the field date and then in _search ask for stored_field date instead of default _source you will get the converted value.

[markpavey]

Thanks for the explanation, that makes sense.