Fixed #26786 -- Avoided redundant max value validators on integer fields.

django/db/models/fields/__init__.py

@@ -1812,14 +1812,22 @@ class IntegerField(Field):
     def validators(self):
         # These validators can't be added at field initialization time since
         # they're based on values retrieved from `connection`.
-        range_validators = []
+        validators_ = super(IntegerField, self).validators
         internal_type = self.get_internal_type()
         min_value, max_value = connection.ops.integer_field_range(internal_type)
         if min_value is not None:
-            range_validators.append(validators.MinValueValidator(min_value))
+            for validator in validators_:
+                if isinstance(validator, validators.MinValueValidator) and validator.limit_value >= min_value:
+                    break
+            else:
+                validators_.append(validators.MinValueValidator(min_value))
         if max_value is not None:
-            range_validators.append(validators.MaxValueValidator(max_value))
-        return super(IntegerField, self).validators + range_validators
+            for validator in validators_:
+                if isinstance(validator, validators.MaxValueValidator) and validator.limit_value <= max_value:
+                    break
+            else:
+                validators_.append(validators.MaxValueValidator(max_value))
+        return validators_
 
     def get_prep_value(self, value):
         value = super(IntegerField, self).get_prep_value(value)

tests/model_fields/test_integerfield.py

@@ -90,6 +90,35 @@ class IntegerFieldTests(TestCase):
             instance.value = max_value
             instance.full_clean()
 
+    def test_redundant_backend_range_validators(self):
+        """
+        If there are stricter validators than the ones from the database
+        backend then the backend validators aren't added.
+        """
+        min_backend_value, max_backend_value = self.backend_range
+
+        if min_backend_value is not None:
+            min_custom_value = min_backend_value + 1
+            ranged_value_field = self.model._meta.get_field('value').__class__(
+                validators=[validators.MinValueValidator(min_custom_value)]
+            )
+            field_range_message = validators.MinValueValidator.message % {
+                'limit_value': min_custom_value,
+            }
+            with self.assertRaisesMessage(ValidationError, "[%r]" % field_range_message):
+                ranged_value_field.run_validators(min_backend_value - 1)
+
+        if max_backend_value is not None:
+            max_custom_value = max_backend_value - 1
+            ranged_value_field = self.model._meta.get_field('value').__class__(
+                validators=[validators.MaxValueValidator(max_custom_value)]
+            )
+            field_range_message = validators.MaxValueValidator.message % {
+                'limit_value': max_custom_value,
+            }
+            with self.assertRaisesMessage(ValidationError, "[%r]" % field_range_message):
+                ranged_value_field.run_validators(max_backend_value + 1)
+
     def test_types(self):
         instance = self.model(value=0)
         self.assertIsInstance(instance.value, six.integer_types)