Renaming fileds in nested json

I have a json like:

{"doc_id": 1, "name": "John", "traveller": { "field_1": "Johnny" }}

and would like to have it loaded like this:
doc_id => doc_id
name - ignored
traveller.field_1 => name_1

I wrote a config file which obviously doesn't work:

filter {
mutate {
remove_field => [ "name" ]
replace => { "name" => "%{traveller.field_1}" }}

but, the end result in ES is still:

"_source": {
"doc_id": 1,
"traveller": {
"field_1": "Johnny"

what have I missed?
as Logstash cannot load nested JSON element into another type/entity, I would like to filter out outer elements, and load inner elements into a chosen entity.


If you use the correct [field][subfield] syntax for nested fields I think it'll work.