retrieve only a specific _index documents in the hits of elasticsearch when querying on multiple indices

Question

I am querying on two indices in one query of elasticsearch so I can aggregate on both of them at once. The problem is that I want only one of the indices documents to be in the hits and not both of them. Hence I would like to filter on the _index field in the query.

Query

http://localhost:9200/products,stores/_search

{
    query: {
        match_all: {}
    },
    aggs = {
        stores : { terms: { field: 'store_name' } }
    }
}

Sample Output

{"hits" :[{"_index": "products",
 "_type": "_doc",
 "_id": "PFS0OTD5UE",
 "_score": 123.057205,
 "_source": {}},

{"_index": "stores",
 "_type": "_doc",
 "_id": "SXBT3ER",
 "_score": 53.057205,
 "_source": {}}]}

I want to only retrieve the product index.

Answer 1

It is definitely possible by using post_filter:

POST products,stores/_search
{
  "query": {
    "match_all": {}
  },
  "aggs": {
    "stores": {
      "terms": {
        "field": "store_name"
      }
    }
  },
  "post_filter": {
    "term": {
      "_index": "products"
    }
  }
}

The aggregation will run on all documents from both indexes, but only the documents from products will be returned in the hits.