Rename "fields" search parameter to "stored_fields"

https://www.elastic.co/guide/en/elasticsearch/reference/5.x/breaking_50_search_changes.html#_literal_fields_literal_parameter

wagtail/wagtailsearch/backends/elasticsearch.py

@@ -416,6 +416,8 @@ class ElasticsearchSearchQuery(BaseSearchQuery):
 
 
 class ElasticsearchSearchResults(BaseSearchResults):
+    fields_param_name = 'fields'
+
     def _get_es_body(self, for_count=False):
         body = {
             'query': self.query.get_query()
@@ -435,10 +437,11 @@ class ElasticsearchSearchResults(BaseSearchResults):
             index=self.backend.get_index_for_model(self.query.queryset.model).name,
             body=self._get_es_body(),
             _source=False,
-            fields='pk',
             from_=self.start,
         )
 
+        params[self.fields_param_name] = 'pk'
+
         # Add size if set
         if self.stop is not None:
             params['size'] = self.stop - self.start

wagtail/wagtailsearch/backends/elasticsearch5.py

@@ -1,7 +1,8 @@
 from __future__ import absolute_import, unicode_literals
 
 from .elasticsearch2 import (
-    Elasticsearch2Mapping, Elasticsearch2SearchBackend, Elasticsearch2SearchQuery)
+    Elasticsearch2Mapping, Elasticsearch2SearchBackend, Elasticsearch2SearchQuery,
+    Elasticsearch2SearchResults)
 
 
 class Elasticsearch5Mapping(Elasticsearch2Mapping):
@@ -14,9 +15,14 @@ class Elasticsearch5SearchQuery(Elasticsearch2SearchQuery):
     mapping_class = Elasticsearch5Mapping
 
 
+class Elasticsearch5SearchResults(Elasticsearch2SearchResults):
+    fields_param_name = 'stored_fields'
+
+
 class Elasticsearch5SearchBackend(Elasticsearch2SearchBackend):
     mapping_class = Elasticsearch5Mapping
     query_class = Elasticsearch5SearchQuery
+    results_class = Elasticsearch5SearchResults
 
 
 SearchBackend = Elasticsearch5SearchBackend

wagtail/wagtailsearch/tests/test_elasticsearch5_backend.py

@@ -603,7 +603,7 @@ class TestElasticsearch5SearchResults(TestCase):
             from_=0,
             body={'query': 'QUERY'},
             _source=False,
-            fields='pk',
+            stored_fields='pk',
             index='wagtail__searchtests_searchtest'
         )
 
@@ -619,7 +619,7 @@ class TestElasticsearch5SearchResults(TestCase):
             from_=10,
             body={'query': 'QUERY'},
             _source=False,
-            fields='pk',
+            stored_fields='pk',
             index='wagtail__searchtests_searchtest',
             size=1
         )
@@ -635,7 +635,7 @@ class TestElasticsearch5SearchResults(TestCase):
             from_=1,
             body={'query': 'QUERY'},
             _source=False,
-            fields='pk',
+            stored_fields='pk',
             index='wagtail__searchtests_searchtest',
             size=3
         )
@@ -651,7 +651,7 @@ class TestElasticsearch5SearchResults(TestCase):
             from_=10,
             body={'query': 'QUERY'},
             _source=False,
-            fields='pk',
+            stored_fields='pk',
             index='wagtail__searchtests_searchtest',
             size=10
         )
@@ -668,7 +668,7 @@ class TestElasticsearch5SearchResults(TestCase):
             from_=20,
             body={'query': 'QUERY'},
             _source=False,
-            fields='pk',
+            stored_fields='pk',
             index='wagtail__searchtests_searchtest',
             size=1
         )