title: ElasticSearch: Is it possible to use dfs_query_then_fetch with the explain API?
body: <p>Did the <code>Explain</code> endpoint ever support <code>search_type: dfs_query_then_fetch</code>? If it does now (I'm on 7.1), how do I specify it?</p>
  
  <p>I was thrown for a loop when using the <code>Explain</code> API on two identical documents, but seeing different score calculations. Learning the documents lived in different shards, and that the TF/IDF inputs were calculated per-shard explained the difference. Using <code>dfs_query_then_fetch</code> on the <code>Search</code> API normalized the scores, but the ElasticSearch .net client (both LowLevel and NEST) don't appear to expose a way to specify it for calls to the <code>Explain</code> API.</p>
  
  <p>I also tried to form a request manually, passing it as a querystring or request body parameter. Both fail saying the argument is invalid. I thought perhaps the <code>Explain</code> endpoint didn't offer a way to specify <code>dfs_query_then_fetch</code>, but digging through some old issues it appears that it at least did at some point:</p>
  
  <p><a href="https://github.com/elastic/elasticsearch/issues/2612" rel="nofollow noreferrer">https://github.com/elastic/elasticsearch/issues/2612</a></p>