[1.7.x] Replaced vendor checks by three feature flags.

Backport of c70a61eb from master

django/db/backends/__init__.py

@@ -575,6 +575,7 @@ class BaseDatabaseFeatures(object):
     can_return_id_from_insert = False
     has_bulk_insert = False
     uses_savepoints = False
+    can_release_savepoints = True
     can_combine_inserts_with_and_without_auto_increment_pk = False
 
     # If True, don't use integer foreign keys referring to, e.g., positive
@@ -610,6 +611,8 @@ class BaseDatabaseFeatures(object):
     supports_subqueries_in_group_by = True
     supports_bitwise_or = True
 
+    supports_binary_field = True
+
     # Do time/datetime fields have microsecond precision?
     supports_microsecond_precision = True
 
@@ -703,6 +706,9 @@ class BaseDatabaseFeatures(object):
     # statements before executing them?
     requires_sqlparse_for_splitting = True
 
+    # Suffix for backends that don't support "SELECT xxx;" queries.
+    bare_select_suffix = ''
+
     def __init__(self, connection):
         self.connection = connection
 

django/db/backends/mysql/base.py

@@ -172,6 +172,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_select_for_update_nowait = False
     supports_forward_references = False
     supports_long_model_names = False
+    # XXX MySQL DB-API drivers currently fail on binary data on Python 3.
+    supports_binary_field = six.PY2
     supports_microsecond_precision = False
     supports_regex_backreferencing = False
     supports_date_lookup_using_string = False

django/db/backends/oracle/base.py

@@ -96,6 +96,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     needs_datetime_string_cast = False
     interprets_empty_strings_as_nulls = True
     uses_savepoints = True
+    can_release_savepoints = False
     has_select_for_update = True
     has_select_for_update_nowait = True
     can_return_id_from_insert = True
@@ -116,6 +117,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     requires_literal_defaults = True
     connection_persists_old_columns = True
     closed_cursor_error_class = InterfaceError
+    bare_select_suffix = " FROM DUAL"
 
 
 class DatabaseOperations(BaseDatabaseOperations):

tests/admin_views/tests.py

@@ -3939,8 +3939,7 @@ class UserAdminTest(TestCase):
         ContentType.objects.clear_cache()
 
         expected_queries = 10
-        # Oracle doesn't implement "RELEASE SAVPOINT", see #20387.
+        if not connection.features.can_release_savepoints:
-        if connection.vendor == 'oracle':
             expected_queries -= 1
 
         with self.assertNumQueries(expected_queries):
@@ -3982,8 +3981,7 @@ class GroupAdminTest(TestCase):
         g = Group.objects.create(name="test_group")
 
         expected_queries = 8
-        # Oracle doesn't implement "RELEASE SAVPOINT", see #20387.
+        if not connection.features.can_release_savepoints:
-        if connection.vendor == 'oracle':
             expected_queries -= 1
 
         with self.assertNumQueries(expected_queries):

tests/backends/tests.py

@@ -131,7 +131,6 @@ class SQLiteTests(TestCase):
             self.assertRaises(NotImplementedError,
                 models.Item.objects.all().aggregate, aggregate('last_modified'))
 
-
     def test_convert_values_to_handle_null_value(self):
         convert_values = DatabaseOperations(connection).convert_values
         self.assertIsNone(convert_values(None, AutoField(primary_key=True)))
@@ -464,9 +463,7 @@ class EscapingChecks(TestCase):
     EscapingChecksDebug test case, to also test CursorDebugWrapper.
     """
 
-    # For Oracle, when you want to select a value, you need to specify the
+    bare_select_suffix = connection.features.bare_select_suffix
-    # special pseudo-table 'dual'; a select with no from clause is invalid.
-    bare_select_suffix = " FROM DUAL" if connection.vendor == 'oracle' else ""
 
     def test_paramless_no_escaping(self):
         cursor = connection.cursor()

tests/model_fields/tests.py

@@ -605,6 +605,7 @@ class FileFieldTests(unittest.TestCase):
 class BinaryFieldTests(test.TestCase):
     binary_data = b'\x00\x46\xFE'
 
+    @test.skipUnlessDBFeature('supports_binary_field')
     def test_set_and_retrieve(self):
         data_set = (self.binary_data, six.memoryview(self.binary_data))
         for bdata in data_set:
@@ -619,10 +620,6 @@ class BinaryFieldTests(test.TestCase):
             # Test default value
             self.assertEqual(bytes(dm.short_data), b'\x08')
 
-    if connection.vendor == 'mysql' and six.PY3:
-        # Existing MySQL DB-API drivers fail on binary data.
-        test_set_and_retrieve = unittest.expectedFailure(test_set_and_retrieve)
-
     def test_max_length(self):
         dm = DataModel(short_data=self.binary_data * 4)
         self.assertRaises(ValidationError, dm.full_clean)

tests/serializers_regress/tests.py

@@ -10,7 +10,7 @@ from __future__ import unicode_literals
 
 import datetime
 import decimal
-from unittest import skip, skipUnless
+from unittest import skipUnless
 import warnings
 
 try:
@@ -24,7 +24,7 @@ from django.core.serializers.base import DeserializationError
 from django.core.serializers.xml_serializer import DTDForbidden
 from django.db import connection, models
 from django.http import HttpResponse
-from django.test import TestCase
+from django.test import skipUnlessDBFeature, TestCase
 from django.utils import six
 from django.utils.functional import curry
 
@@ -481,8 +481,7 @@ def serializerTest(format, self):
     for klass, count in instance_count.items():
         self.assertEqual(count, klass.objects.count())
 
-if connection.vendor == 'mysql' and six.PY3:
+serializerTest = skipUnlessDBFeature('supports_binary_field')(serializerTest)
-    serializerTest = skip("Existing MySQL DB-API drivers fail on binary data.")(serializerTest)
 
 
 def naturalKeySerializerTest(format, self):