How to aggregate a term before it's used to filter results

[Guy_Bowden]

I have a field containing simple tags for example. I'd like to be able to use those tags to perform a faceted search but have the tag counters showing the counts of matches before the tag is used as a filter.

e.g.

Foo (20)
*Bar (25)*  <--- selected tag
Bof (23) <--- if I select this tag 'Bar' is deselected and I get 23 results (which may or may not have documents tagged `Bar`
Bif (19) 

At the moment I have a search that looks like this:

{
   "query":{
      "bool":{
         "filter":[
            {
               "term":{
                  "tag":"Bar"
               }
            }
         ]
      }
   },
   "aggs":{
      "by_tag":{
         "terms":{
            "field":"tag",
            "size":0
         }
      }
   }
}

This will give me counts for all document tags where the document is tagged Bar already

I could perform multiple searches to get the aggregations, but wondered if there was a simpler way?

[Mark_Harwood]

Check out the post_filter expression to apply additional filters to your search results but which don't filter any aggregations.

[Guy_Bowden]

Thanks Mark - a little more investigation has shown me the 'global' keyword and filter on aggregations. I have implemented this by copying the overall search filter and removing the one I'm interested in for each aggregation.

i couldn't see how to use post_filter aside from a simple use-case where I didn't want any filters applied to any of the aggregations, whereas I need to essentially have all my filters applied except for the filter applied on my aggregation field.