Filtering aggregation results - elasticsearch

Question

This question is a subquestion of this question. Posting as a separate question for attention.
Sample Docs:
{
"id":1,
"product":"p1",
"cat_ids":[1,2,3]
}
{
"id":2,
"product":"p2",
"cat_ids":[3,4,5]
}
{
"id":3,
"product":"p3",
"cat_ids":[4,5,6]
}
Ask: To get products belonging to a particular category. e.g cat_id = 3
Query:
GET product/_search
{
"size": 0,
"aggs": {
"cats": {
"terms": {
"field": "cats",
"size": 10
},"aggs": {
"products": {
"terms": {
"field": "name.keyword",
"size": 10
}
}
}
}
}
}
Question:
How to filter the aggregated result for cat_id = 3 here. I tried bucket_selector as well but it is not working.
Note: Due to multi-value of cat_ids filtering and then aggregation isn't working

Answer 1

You can filter values, on the basis of which buckets will be created.
It is possible to filter the values for which buckets will be created.
This can be done using the include and exclude parameters which are
based on regular expression strings or arrays of exact values.
Additionally, include clauses can filter using partition expressions.
Adding a working example with index data, search query, and search result
Index Data:
{
"id":1,
"product":"p1",
"cat_ids":[1,2,3]
}
{
"id":2,
"product":"p2",
"cat_ids":[3,4,5]
}
{
"id":3,
"product":"p3",
"cat_ids":[4,5,6]
}
Search Query:
{
"size": 0,
"aggs": {
"cats": {
"terms": {
"field": "cat_ids",
"include": [ <-- note this
3
]
},
"aggs": {
"products": {
"terms": {
"field": "product.keyword",
"size": 10
}
}
}
}
}
}
Search Result:
"aggregations": {
"cats": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": 3,
"doc_count": 2,
"products": {
"doc_count_error_upper_bound": 0,
"sum_other_doc_count": 0,
"buckets": [
{
"key": "p1",
"doc_count": 1
},
{
"key": "p2",
"doc_count": 1
}
]
}
}
]
}