Elasticsearch: retrieve only document _id where field doesn't exist - elasticsearch

Question

I would like to retrieve all document _ids (without other fields) where field "name" doesn't exist:
I know I can search for where field "name" doesn't exist like this:
"query": {
"bool": {
"must_not": {
"exists": {
"field": "name"
}
}
}
}
and I think that to get the _id of the document only without any fields i need to use (correct me if I'm wrong):
"fields": []
How do I combine these 2 parts to make a query that works?

Answer 1

You can just add _source and set to false as Elasticsearch will return the entire JSON object in that field by default
"_source": false,
"query":{
...
}
and this will retrieve just the metadata from your specified index, so your hits array will contain _index, _type, _id and _score for each result
e.g
{
"took" : 11,
"timed_out" : false,
"_shards" : {
"total" : 12,
"successful" : 12,
"skipped" : 0,
"failed" : 0
},
"hits" : {
"total" : {
"value" : 20,
"relation" : "eq"
},
"max_score" : 1.0,
"hits" : [
{
"_index" : "filebeat-7.8.1-2021.01.28",
"_type" : "_doc"
"_id" : "SomeUniqeuId86aa",
"_score" : 1.0
},
{
"_index" : "filebeat-7.8.1-2021.01.28",
"_type" : "_doc"
"_id" : "An0therrUniqueiD",
"_score" : 1.0
}
]
}
}