Merge pull request #4679 from vespa-engine/johsol/json-query-language-fields

Johsol/json query language fields

Author: hmusum

en/reference/api/query.html

@@ -2331,7 +2331,7 @@ <h3>Error code to status code mapping</h3>
 <h2 id="select.json">select</h2>
 <p>
   A <code>select</code> query is equivalent in structure to YQL, written in JSON.
-  Contains subparameters <code>where</code> and <code>grouping</code>.
+  Contains subparameters <code>where</code>, <code>grouping</code> and <code>fields</code>.
 </p>
 <table class="table">
   <thead>
@@ -2368,5 +2368,18 @@ <h2 id="select.json">select</h2>
       </p>
     </td>
   </tr>
+  <tr>
+    <th>fields</th>
+    <td></td>
+    <td>String</td>
+    <td></td>
+    <td>
+      <p id="select.fields">
+        A JSON array of <a href="../../querying/document-summaries.html#selecting-summary-fields-in-yql">summary field</a>
+        names to include in each hit. Equivalent to the field list in a YQL <code>select</code> clause.
+        Refer to the <a href="../querying/json-query-language">select reference</a> for details.
+      </p>
+    </td>
+  </tr>
   </tbody>
 </table>

en/reference/querying/json-query-language.md

@@ -16,7 +16,8 @@ The query has JSON syntax, and can be used with queries that are executed with H
 ```json
 "select" : {
   "where" : {...},
-  "grouping" : {...}
+  "grouping" : {...},
+  "fields" : [...]
 }
 ```
 
@@ -91,6 +92,34 @@ which is equivalent with the YQL.
 
 
 
+### Fields
+
+Available since {% include version.html version="8.680.18" %}.
+
+The `fields` parameter restricts which
+[summary fields](../../querying/document-summaries.html#selecting-summary-fields-in-yql)
+are included in each hit. It is a JSON array of field names, and is equivalent
+to the field list in a YQL `select` clause.
+
+YQL: `select id, title from sources * where title contains 'madonna'`.
+
+Equivalent JSON:
+
+```json
+{
+  "select": {
+    "fields": ["id", "title"],
+    "where": {
+      "contains": ["title", "madonna"]
+    }
+  }
+}
+```
+
+If `fields` is omitted or empty, all fields of the chosen
+[document summary class](../../querying/document-summaries.html) are returned.
+
+
 ### Grouping
 
 One or more [grouping statements](../../querying/grouping.html) can be set as a JSON array in the `grouping` field.