ElasticSearch: getting facets from all results with filter query

Question

I don't know whether the title of this question is clear enough.

I have a text search with language filter in the left pane in ElasticSearch. When a specific language filter is selected in the left pane from search results (from a query), I still want to get the language facets from all search results from the query. I know this is possible in Solr but I am not sure whether this is doable in ElasticSearch.

Answer 1

Yes, you can achieve this by using post_filter instead of a normal filter. What post_filter does is to filter the documents after the aggregations have been computed on the full data set.

So instead of this:

{
  "query": {
    "bool": {
      "filter": {
        "term": {
          "some_field": "some_value"
        }
      }
    }
  },
  "aggs": {
    "languages": {
      "terms": {
        "field": "language"
      }
    }
  }
}

Do this:

{
  "post_filter": {
    "term": {
      "some_field": "some_value"
    }
  },
  "aggs": {
    "languages": {
      "terms": {
        "field": "language"
      }
    }
  }
}