Fix pagination when asking for the last page on a query that matches no records

CHANGELOG.md

@@ -5,6 +5,7 @@ Unreleased
 ----------
 - Extend date field range (trthhrtz)
 - Fix parsing of server errors in ClickHouse v19.3.3+
+- Fix pagination when asking for the last page on a query that matches no records
 
 v1.0.4
 ------

src/infi/clickhouse_orm/database.py

@@ -285,7 +285,7 @@ class Database(object):
         count = self.count(model_class, conditions)
         pages_total = int(ceil(count / float(page_size)))
         if page_num == -1:
-            page_num = pages_total
+            page_num = max(pages_total, 1)
         elif page_num < 1:
             raise ValueError('Invalid page number: %d' % page_num)
         offset = (page_num - 1) * page_size
@@ -296,7 +296,7 @@ class Database(object):
         query += ' LIMIT %d, %d' % (offset, page_size)
         query = self._substitute(query, model_class)
         return Page(
-            objects=list(self.select(query, model_class, settings)),
+            objects=list(self.select(query, model_class, settings)) if count else [],
             number_of_objects=count,
             pages_total=pages_total,
             number=page_num,

tests/test_database.py

@@ -112,6 +112,14 @@ class DatabaseTestCase(TestCaseWithData):
             self.assertEqual([obj.to_tsv() for obj in page_a.objects],
                               [obj.to_tsv() for obj in page_b.objects])
 
+    def test_pagination_empty_page(self):
+        for page_num in (-1, 1, 2):
+            page = self.database.paginate(Person, 'first_name, last_name', page_num, 10, conditions="first_name = 'Ziggy'")
+            self.assertEqual(page.number_of_objects, 0)
+            self.assertEqual(page.objects, [])
+            self.assertEqual(page.pages_total, 0)
+            self.assertEqual(page.number, max(page_num, 1))
+
     def test_pagination_invalid_page(self):
         self._insert_and_check(self._sample_data(), len(data))
         for page_num in (0, -2, -100):