Retrieving field values from field data

[rashidkpc]

There are situations where it is advantageous to retrieve not the field as it was stored, but rather the value that was indexed. The example that spurred this was dates.

Dates are stored in a variety of formats, but are always normalized into a long for indexing. However, when retrieving dates they come back as stringw that need to be parsed into the language's native date object, which requires knowing their format. Field data's normalized long could be parsed into a date object without needing to know the original source field's format.

The proposed feature would allow the user to specify that they want the field value to be retrieved from field data using the format: _fielddata.fieldname, much like we support _source.fieldname.

Eg:

{
    "query": { 
        "match_all": {
        }
    },
    "fields": ["_fielddata.user.id"]
}

[javanna]

Closing, this was implemented in #4492 and #4728 .

[rashidkpc]

Awesome, thanks!