title: Elasticsearch - give negative boost to documents without a certain field
body: <p>I'm working on a query, the basic filtered multi match query is working as planned, it returns the documents i want.</p>
  
  <p>The issue is that a want to boost results which have a certain string field with ex. 0.5, or in this example give results which don't have this field 'traded_as' a negative boost of 1.0.</p>
  
  <p>Cannot get the filter - boost - must - exists/missing to work as i want.</p>
  
  <p>It this the correct approach on this issue?</p>
  
  <p>Using elasticsearch 1.5.2</p>
  
  <pre><code>{
  "query": {
      "filtered": {
          "query": {
             "multi_match": {
                 "query": "something",
                 "fields": ["title", "url", "description"]
             }
          },
          "filter": {
             "bool": {
                  "must": {
                      "missing": {
                          "field": "marked_for_deletion"
                      }
                  }
              }
          }
      }
  },
  "boosting": {
      "positive": {
          "filter": {
              "bool": {
                  "must": {
                      "exists": {
                          "field": "traded_as"                            
                      }
                  }
              }
          }
      },
      "negative": {
          "filter": {
             "bool": {
                  "must": {
                      "missing": {
                          "field": "traded_as"
                      }
                  }
              }
          }
      },
      "negative_boost": 1.0
  }
  }
  </code></pre>