[Postgres_search] Adds a default ordering when ranking of objects is the same.

CHANGELOG.txt

@@ -8,6 +8,8 @@ Changelog
  * Fix: Using `order_by_relevance=False` when searching with PostgreSQL now works (Mitchel Cabuloy)
  * Fix: Inline panel first and last sorting arrows correctly hidden in non-default tabs (Matt Westcott)
  * Fix: `WAGTAILAPI_LIMIT_MAX` now accepts None to disable limiting (jcronyn)
+ * Fix: In PostgreSQL, new default ordering when ranking of objects is the same (Bertrand Bordage)
+
 
 1.12 LTS (21.08.2017)
 ~~~~~~~~~~~~~~~~~~~~~

docs/releases/1.13.rst

@@ -22,6 +22,7 @@ Bug fixes
  * Using ``order_by_relevance=False`` when searching with PostgreSQL now works (Mitchel Cabuloy)
  * Inline panel first and last sorting arrows correctly hidden in non-default tabs (Matt Westcott)
  * ``WAGTAILAPI_LIMIT_MAX`` now accepts None to disable limiting (jcronyn)
+ * In PostgreSQL, new default ordering when ranking of objects is the same (Bertrand Bordage)
 
 
 Upgrade considerations

wagtail/contrib/postgres_search/backend.py

@@ -246,12 +246,13 @@ class PostgresSearchQuery(BaseSearchQuery):
 
     def search_in_index(self, queryset, search_query, start, stop):
         index_entries = self.get_in_index_queryset(queryset, search_query)
-        order_sql = ''
         values = ['typed_pk']
         if self.order_by_relevance:
             index_entries = index_entries.rank(search_query)
             values.append('rank')
-            order_sql = 'ORDER BY index_entry.rank DESC'
+            order_sql = 'index_entry.rank DESC, id ASC'
+        else:
+            order_sql = 'id ASC'
         index_sql, index_params = get_sql(
             index_entries.annotate_typed_pk()
             .values(*values)
@@ -262,7 +263,7 @@ class PostgresSearchQuery(BaseSearchQuery):
             SELECT obj.*
             FROM (%s) AS index_entry
             INNER JOIN (%s) AS obj ON obj."%s" = index_entry.typed_pk
-            %s
+            ORDER BY %s
             OFFSET %%s LIMIT %%s;
             """ % (index_sql, model_sql, get_pk_column(model), order_sql)
         limits = (start, None if stop is None else stop - start)

wagtail/wagtailsearch/tests/test_backends.py

@@ -200,6 +200,30 @@ class BackendTests(WagtailTestUtils):
             set(unsorted_results),
             {self.testa, self.testb, self.testc.searchtest_ptr})
 
+    def test_same_rank_pages(self):
+        """
+        Checks that results with a same ranking cannot be found multiple times
+        across pages (see issue #3729).
+        """
+        same_rank_objects = set()
+        try:
+            for i in range(10):
+                obj = models.SearchTest.objects.create(title='Rank %s' % i)
+                self.backend.add(obj)
+                same_rank_objects.add(obj)
+            self.refresh_index()
+
+            results = self.backend.search('Rank', models.SearchTest)
+            results_across_pages = set()
+            for i, obj in enumerate(same_rank_objects):
+                results_across_pages.add(results[i:i + 1][0])
+            self.assertSetEqual(results_across_pages, same_rank_objects)
+        finally:
+            for obj in same_rank_objects:
+                self.backend.delete(obj)
+                obj.delete()
+            self.refresh_index()
+
     def test_delete(self):
         # Delete one of the objects
         self.backend.delete(self.testa)