Fixed #28293 -- Fixed union(), intersection(), and difference() when combining with an EmptyQuerySet.

felixxm · web-flow · commit 82175ead723f · 2017-06-13T08:16:16.000+02:00
Thanks Jon Dufresne for the report and Tim Graham for the review.
diff --git a/django/db/models/query.py b/django/db/models/query.py
@@ -818,12 +818,25 @@ def _combinator_query(self, combinator, *other_qs, all=False):
         return clone
 
     def union(self, *other_qs, all=False):
+        # If the query is an EmptyQuerySet, combine all nonempty querysets.
+        if isinstance(self, EmptyQuerySet):
+            qs = [q for q in other_qs if not isinstance(q, EmptyQuerySet)]
+            return qs[0]._combinator_query('union', *qs[1:], all=all) if qs else self
         return self._combinator_query('union', *other_qs, all=all)
 
     def intersection(self, *other_qs):
+        # If any query is an EmptyQuerySet, return it.
+        if isinstance(self, EmptyQuerySet):
+            return self
+        for other in other_qs:
+            if isinstance(other, EmptyQuerySet):
+                return other
         return self._combinator_query('intersection', *other_qs)
 
     def difference(self, *other_qs):
+        # If the query is an EmptyQuerySet, return it.
+        if isinstance(self, EmptyQuerySet):
+            return self
         return self._combinator_query('difference', *other_qs)
 
     def select_for_update(self, nowait=False, skip_locked=False):
diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
@@ -390,7 +390,7 @@ def get_combinator_sql(self, combinator, all):
         features = self.connection.features
         compilers = [
             query.get_compiler(self.using, self.connection)
-            for query in self.query.combined_queries
+            for query in self.query.combined_queries if not query.is_empty()
         ]
         if not features.supports_slicing_ordering_in_compound:
             for query, compiler in zip(self.query.combined_queries, compilers):
diff --git a/docs/releases/1.11.3.txt b/docs/releases/1.11.3.txt
@@ -29,3 +29,6 @@ Bugfixes
 
 * Fixed crash in admin's inlines when a model has an inherited non-editable
   primary key (:ticket:`27967`).
+
+* Fixed ``QuerySet.union()``, ``intersection()``, and ``difference()`` when
+  combining with an ``EmptyQuerySet`` (:ticket:`28293`).
diff --git a/tests/queries/test_qs_combinators.py b/tests/queries/test_qs_combinators.py
@@ -42,6 +42,31 @@ def test_union_distinct(self):
         self.assertEqual(len(list(qs1.union(qs2, all=True))), 20)
         self.assertEqual(len(list(qs1.union(qs2))), 10)
 
+    @skipUnlessDBFeature('supports_select_intersection')
+    def test_intersection_with_empty_qs(self):
+        qs1 = Number.objects.all()
+        qs2 = Number.objects.none()
+        self.assertEqual(len(qs1.intersection(qs2)), 0)
+        self.assertEqual(len(qs2.intersection(qs1)), 0)
+        self.assertEqual(len(qs2.intersection(qs2)), 0)
+
+    @skipUnlessDBFeature('supports_select_difference')
+    def test_difference_with_empty_qs(self):
+        qs1 = Number.objects.all()
+        qs2 = Number.objects.none()
+        self.assertEqual(len(qs1.difference(qs2)), 10)
+        self.assertEqual(len(qs2.difference(qs1)), 0)
+        self.assertEqual(len(qs2.difference(qs2)), 0)
+
+    def test_union_with_empty_qs(self):
+        qs1 = Number.objects.all()
+        qs2 = Number.objects.none()
+        self.assertEqual(len(qs1.union(qs2)), 10)
+        self.assertEqual(len(qs2.union(qs1)), 10)
+        self.assertEqual(len(qs2.union(qs1, qs1, qs1)), 10)
+        self.assertEqual(len(qs2.union(qs1, qs1, all=True)), 20)
+        self.assertEqual(len(qs2.union(qs2)), 0)
+
     def test_limits(self):
         qs1 = Number.objects.all()
         qs2 = Number.objects.all()

Original file line number	Diff line number	Diff line change
`@@ -390,7 +390,7 @@ def get_combinator_sql(self, combinator, all):`
`390`	`390`	`features = self.connection.features`
`391`	`391`	`compilers = [`
`392`	`392`	`query.get_compiler(self.using, self.connection)`
`393`		`- for query in self.query.combined_queries`
	`393`	`+ for query in self.query.combined_queries if not query.is_empty()`
`394`	`394`	`]`
`395`	`395`	`if not features.supports_slicing_ordering_in_compound:`
`396`	`396`	`for query, compiler in zip(self.query.combined_queries, compilers):`