Ticket #27729: evaluate.diff

django/db/models/query.py

@@ -992 +992 @@
         clone._db = alias
         return clone
 
+    def evaluate(self):
+        """
+        Returns a new, evaluated QuerySet instance.
+        """
+        clone = self._clone()
+        clone._fetch_all()
+        return clone
+
+
     ###################################
     # PUBLIC INTROSPECTION ATTRIBUTES #
     ###################################

tests/queries/tests.py

@@ -8 +8 @@
 
 from django.core.exceptions import EmptyResultSet, FieldError
 from django.db import DEFAULT_DB_ALIAS, connection
-from django.db.models import Count, F, Q
+from django.db.models import Count, F, Q, QuerySet
 from django.db.models.sql.constants import LOUTER
 from django.db.models.sql.where import NothingNode, WhereNode
 from django.test import TestCase, skipUnlessDBFeature
@@ -3797 +3797 @@
             set(Ticket23605A.objects.filter(qy).values_list('pk', flat=True))
         )
         self.assertSequenceEqual(Ticket23605A.objects.filter(qx), [a2])
+
+
+class EvaluateMethodTests(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        Number.objects.create(num=4)
+        Number.objects.create(num=4)
+        Number.objects.create(num=8)
+
+    def test_evaluate_allows_chain_methods(self):
+        """
+        Tests that evaluate indeed returns a QuerySet.
+        """
+        numbers = Number.objects.evaluate()
+        self.assertIsInstance(numbers, QuerySet)
+
+    def test_evaluate_populates_result_cache(self):
+        """
+        Tests that evaluate() populates the result cache.
+        """
+        numbers = Number.objects.filter(num__lte=6)
+        self.assertIsNone(numbers._result_cache)
+        numbers = numbers.evaluate()
+        self.assertTrue(numbers._result_cache)
+
+    def test_evaluate_does_not_query_database(self):
+        """
+        Tests that subsequent QuerySet operations does not query the database after evaluate have been called.
+        """
+        def test_function():
+            numbers = Number.objects.filter(num__lte=6)
+            numbers = numbers.evaluate()
+            numbers = numbers.filter(num__lte=5)
+
+        self.assertNumQueries(1, lambda: test_function())