[1.8.x] Fixed #25767 -- Fixed data truncation possibility with Positive(Small)IntegerField on MySQL.

Backport of 710e11d076 from master

django/db/backends/mysql/operations.py

@@ -13,8 +13,8 @@ class DatabaseOperations(BaseDatabaseOperations):
 
     # MySQL stores positive fields as UNSIGNED ints.
     integer_field_ranges = dict(BaseDatabaseOperations.integer_field_ranges,
-        PositiveSmallIntegerField=(0, 4294967295),
-        PositiveIntegerField=(0, 18446744073709551615),
+        PositiveSmallIntegerField=(0, 65535),
+        PositiveIntegerField=(0, 4294967295),
     )
 
     def date_extract_sql(self, lookup_type, field_name):

docs/releases/1.8.7.txt

@@ -46,3 +46,8 @@ Bugfixes
 * Fixed ``set_FOO_order()`` crash when the ``ForeignKey`` of a model with
   ``order_with_respect_to`` references a model with a ``OneToOneField``
   primary key (:ticket:`25786`).
+
+* Fixed incorrect validation for ``PositiveIntegerField`` and
+  ``PositiveSmallIntegerField`` on MySQL resulting in values greater than
+  4294967295 or 65535, respectively, passing validation and being silently
+  truncated by the database (:ticket:`25767`).

tests/model_fields/tests.py

@@ -506,6 +506,12 @@ class IntegerFieldTests(test.TestCase):
     model = IntegerModel
     documented_range = (-2147483648, 2147483647)
 
+    @property
+    def backend_range(self):
+        field = self.model._meta.get_field('value')
+        internal_type = field.get_internal_type()
+        return connection.ops.integer_field_range(internal_type)
+
     def test_documented_range(self):
         """
         Ensure that values within the documented safe range pass validation,
@@ -527,14 +533,34 @@ class IntegerFieldTests(test.TestCase):
         self.assertEqual(qs.count(), 1)
         self.assertEqual(qs[0].value, max_value)
 
+    def test_backend_range_save(self):
+        """
+        Ensure that backend specific range can be saved without corruption.
+        """
+        min_value, max_value = self.backend_range
+
+        if min_value is not None:
+            instance = self.model(value=min_value)
+            instance.full_clean()
+            instance.save()
+            qs = self.model.objects.filter(value__lte=min_value)
+            self.assertEqual(qs.count(), 1)
+            self.assertEqual(qs[0].value, min_value)
+
+        if max_value is not None:
+            instance = self.model(value=max_value)
+            instance.full_clean()
+            instance.save()
+            qs = self.model.objects.filter(value__gte=max_value)
+            self.assertEqual(qs.count(), 1)
+            self.assertEqual(qs[0].value, max_value)
+
     def test_backend_range_validation(self):
         """
         Ensure that backend specific range are enforced at the model
         validation level. ref #12030.
         """
-        field = self.model._meta.get_field('value')
-        internal_type = field.get_internal_type()
-        min_value, max_value = connection.ops.integer_field_range(internal_type)
+        min_value, max_value = self.backend_range
 
         if min_value is not None:
             instance = self.model(value=min_value - 1)