How to specify "fields" in Elasticsearch request "SearchSource" struct

[bjur]

Which version of Elastic are you using?

[x ] elastic.v7 (for Elasticsearch 7.x)
[ ] elastic.v6 (for Elasticsearch 6.x)
[ ] elastic.v5 (for Elasticsearch 5.x)
[ ] elastic.v3 (for Elasticsearch 2.x)
[ ] elastic.v2 (for Elasticsearch 1.x)

Please describe the expected behavior

I would like to achieve the following:
https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html

However looking at the SearchSource struct I can only specify "doc_value" fields and "stored_fields" however I can't seem to find how to specify just "fields" field e.g. from the ES example:

POST my-index-000001/_search
{
"query": {
"match": {
"message": "foo"
}
},
"fields": ["user.id", "@timestamp"],
"_source": false
}

[bjur]

After further search I seem to find the answer (provided by @olivere in another thread https://www.elastic.co/guide/en/elasticsearch/reference/5.2/breaking_50_search_changes.html#_literal_fields_literal_parameter):

The fields parameter has been replaced by stored_fields. The stored_fields parameter will only return stored fields — it will no >longer extract values from the _source

However manually constructing the JSON struct and posting it directly to ES using curl works as expected using "fields" in Elastcisearch 7.x

[olivere]

As stated here, this feature is in beta and probably has not too much to do with the thread mentioned above. It's a bit like FetchSourceContext which allows to include/exclude certain fields, but with the benefit of what's being said in the 2nd paragraph.

[JeremyCraven]

Hey, checking to see if "fields" is still planning on being supported. There is a scenario that we must use fields instead of _source to avoid too_complex_to_determinize_exception. @olivere

[mitar]

This looks now stable and it seems it is also encouraged:

Using fields is typically better
These options are usually not required. Using the fields option is typically the better choice, unless you absolutely need to force loading a stored or docvalue_fields.

It would be nice for #1625 to get merged.

[jnardone]

Just chiming in that we could really use this too