How to diversify the result of top-hits aggregation? - elasticsearch

Question

Let's start with a concrete example. I have a document with these fields:
{
"template": {
"mappings": {
"template": {
"properties": {
"tid": {
"type": "long"
},
"folder_id": {
"type": "long"
},
"status": {
"type": "integer"
},
"major_num": {
"type": "integer"
}
}
}
}
}
}
I want to aggregate the query result by field folder_id, and for each group divided by folder_id, retrieve the top-N documents' _source detail. So i write query DSL like:
GET /template/template/_search
{
"size": 0,
"query": {
"bool": {
"filter": [
{
"term": {
"status": 1
}
}
]
}
},
"aggs": {
"folder": {
"terms": {
"field": "folder_id",
"size": 10
},
"aggs": {
"top_hit":{
"top_hits": {
"size": 5,
"_source": ["major_num"]
}
}
}
}
}
}
However, now comes a requirement that the top hits documents for each folder_id must be diversified on the field major_num. For each folder_id, the top hits documents retrieve by the sub top_hits aggregation under the terms aggregation, must be unique on field major_num, and for each major_num value, return at most 1 document in the sub top hits aggregation result.
top_hits aggregation cannot accept sub-aggregations, so how should i solve the question?

Answer 1

Why not simply adding another terms aggregation on the major_num field ?
GET /template/template/_search
{
"size": 0,
"query": {
"bool": {
"filter": [
{
"term": {
"status": 1
}
}
]
}
},
"aggs": {
"folder": {
"terms": {
"field": "folder_id",
"size": 10
},
"aggs": {
"majornum": {
"terms": {
"field": "major_num",
"size": 10
},
"aggs": {
"top_hit": {
"top_hits": {
"size": 1
}
}
}
}
}
}
}
}