Nested aggregation in nested field? - elasticsearch

Question

I am new to elasticsearch and don't know a lot about aggregations but I have this ES6 mapping:
{
"mappings": {
"test": {
"properties": {
"id": {
"type": "integer"
}
"countries": {
"type": "nested",
"properties": {
"global_id": {
"type": "keyword"
},
"name": {
"type": "text",
"fields": {
"raw": {
"type": "keyword"
}
}
}
}
},
"areas": {
"type": "nested",
"properties": {
"global_id": {
"type": "keyword"
},
"name": {
"type": "text",
"fields": {
"raw": {
"type": "keyword"
}
}
},
"parent_global_id": {
"type": "keyword"
}
}
}
}
}
}
}
How can I get all documents grouped by areas which is then grouped by countries. Also the document has to be returned in full, not just the nested document. Is this even possible ?

Answer 1

1) Aggregation _search query:
first agg by area, with the path as this is nested. Then reverse to the root document and nested agg to country.
{
"size": 0,
"aggs": {
"agg_areas": {
"nested": {
"path": "areas"
},
"aggs": {
"areas_name": {
"terms": {
"field": "areas.name"
},
"aggs": {
"agg_reverse": {
"reverse_nested": {},
"aggs": {
"agg_countries": {
"nested": {
"path": "countries"
},
"aggs": {
"countries_name": {
"terms": {
"field": "countries.name"
}
}
}
}
}
}
}
}
}
}
}
}
2) retrieve documents:
add a tophits inside your aggregation:
https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-metrics-top-hits-aggregation.html
top_hits is slow so you will have to read documentation and adjust size and sort to your context.
...
"terms": {
"field": "areas.name"
},
"aggregations": {
"hits": {
"top_hits": { "size": 100}
}
},
...