Support query and filter in function_score

[sandstrom]

Function score is an excellent addition to ES. However, it doesn't support query + filter, which works in most other parts of ES.

Currently, function_score takes either a filter OR a query, but not both. Allowing support for both query and filter would be good because:

1. It would align better with the rest of ES (it took me a while to figure out why the filter wasn't applied). Overall the API is fairly consistent and well-designed, which I like. Smoothing out this rough edge would make it even better!
2. It would be very useful.

Below is a simple use-case.

# This query is run against two indices, 'users' and 'speakers'.
# But I think the situation would be the same if it was a single index, 
# with two different types in it.
# 
# I get the following error:
# `QueryParsingException[[users] Unknown field [mentioned_at]];`
#
# All speakers has the `mentioned_at` field, and no user has it.

query_body = {
  :query => {
    :bool => {
      :should => [
        {
          :function_score => {
            :query => {
              :multi_match => {
                :query => "MY QUERY HERE",
                :type => :phrase_prefix,
                :fields => ['name']
              }
            },
            :filter => { :type => { :value => 'speaker' } },
            :functions => [
              {
                :gauss => {
                  'mentioned_at' => {
                    :scale => '180d',
                    :offset => '5d',
                    :decay => 0.5,
                  }
                }
              }
            ]
          }
        },
        {
          :filtered => {
            :query => {
              :multi_match => {
                :query => "MY QUERY HERE",
                :type => :phrase_prefix,
                :fields => ['name']
              }
            },
            :filter => { :type => { :value => 'user' } },
          }
        }
      ]
    }
  }
}

Reference

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-function-score-query.html

[clintongormley]

Hi @sandstrom

You can use a filtered query instead, which will do what you need. However, I agree that silently choosing just one of filter or query is incorrect. I see no need why we can't combine both.

@brwe ?

[sandstrom]

@clintongormley Awesome, thanks for looking into this! ⛵

[brwe]

easiest would be to just convert given query and filter to a filtered_query. I'll make a pr shortly.

[sandstrom]

@brwe Awesome!