title: NEST 5.x Fields Usage
body: <p>I have two snippets of code from nest 2.3 that I haven't been able to get to cooperate in the latest 5.0.0-rc3.</p>
  
  <pre><code>var titleField = Infer.Field&lt;Page&gt;(p =&gt; p.Title, 2);
          var metaDescriptionField = Infer.Field&lt;Page&gt;(p =&gt; p.MetaDescription, 1.5);
          var metaKeywordsField = Infer.Field&lt;Page&gt;(p =&gt; p.Keywords, 2);
          var bodyField = Infer.Field&lt;Page&gt;(p =&gt; p.Body);
  
          MultiMatchQuery multiMatchQuery = new MultiMatchQuery()
          {
              Fields = new [] {
                  bodyField, 
                  metaKeywordsField,
                  metaKeywordsField,
                  titleField
              },
              Query = search.Term
          };
  </code></pre>
  
  <p>The build error here is "Cannot implicitly convert Nest.Field[] to Nest.Fields". I can do something like </p>
  
  <pre><code>MultiMatchQuery multiMatchQuery = new MultiMatchQuery()
          {
              Fields = Infer.Fields&lt;Page&gt;(p =&gt; p.Title, p =&gt; p.MetaDescription, p =&gt; p.Keywords, p =&gt; p.Body),
              Query = search.Term
          };
  </code></pre>
  
  <p>But then I lose the field weighting. </p>
  
  <p>Second field useagle I've been having troubles with is </p>
  
  <pre><code>var searchResponse = client.Search&lt;Page&gt;(s =&gt; s
              .MatchAll()
              .From(from)
              .Size(size)
              .Fields(f =&gt; f.Field(fi =&gt; fi.Id).Field(fi =&gt; fi.SourceId))
              );
  </code></pre>
  
  <p>Build error here is 'Nest.SearchDescriptor' does not contain a definition for 'Fields' and no extension method 'Fields' accepting a first argument of type 'Nest.SearchDescriptor' could be found (are you missing a using directive or an assembly reference?</p>
  
  <p>I haven't had any luck with getting something compile-able in the case. </p>