Can I force ES to return dates in epoch_millis format? - elasticsearch

Question

I have this field mapping
"time": {
"type": "date",
"format": "strict_date_optional_time||epoch_millis"
},
and I'm querying documents with this filter:
"range": {
"time": {
"gt": "1473157500000",
"lte": "1473158700000",
"format": "epoch_millis"
}
this works and returns documents, but the result show the time field in a different format:
"time": "2016-09-06T10:25:23.678",
Is it possible to force queries to be returned in epoch_millis?

Answer 1

The _source always returns the data in the original document.
Ideally I feel it maybe more desirable and flexible to convert the _source data to the desired format for presentation or otherwise on the client end.
However for the above use case you could use fielddata_fields.
fielddata_fields would return fields in the format of how the field-data is actually stored which in case of date field happens to be epoch_millis.
From documentation:
Allows to return the field data representation of a field for each hit
Field data fields can work on fields that are not stored. It’s
important to understand that using the fielddata_fields parameter will
cause the terms for that field to be loaded to memory (cached), which
will result in more memory consumption.
Example:
post <index>/_search
{
"fielddata_fields": [
"time"
]
}

Answer 2

ES 6.5 onwards, we need to use docvalue_fields in this specific structure, as the fielddata_fields has been deprecated. E.g. let's say we ingested a json doc of the following format:
{
"#version": "1",
"#timestamp": "2019-01-29T10:01:19.217Z",
"host": "C02NTJRMG3QD",
"message": "hello world!"
}
Now let's execute the following get query with docvalue_fields:
curl -X GET \
http://localhost:9200/myindex/_search \
-H 'Content-Type: application/json' \
-d '{
"query": {
"match_all": {}
},
"docvalue_fields": [
{
"field": "#timestamp",
"format": "epoch_millis"
}
]
}'
And, we'll get the following response:
{
"took": 15,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 1,
"hits": [
{
"_index": "myindex",
"_type": "doc",
"_id": "mY8OmWgBF3ZItz5TVDiL",
"_score": 1,
"_source": {
"#version": "1",
"#timestamp": "2019-01-29T10:01:19.217Z",
"host": "C02NTJRMG3QD",
"message": "hello world!"
},
"fields": {
"#timestamp": [
"1548756079217"
]
}
}
]
}
}