Fixed postgis test database initialization

Refs #20968. Allow querying template_postgis presence without
existing test database.
Thanks Tim Graham for the review.

django/contrib/gis/db/backends/postgis/base.py

 from django.conf import settings
-from django.db.backends.creation import NO_DB_ALIAS
+from django.db.backends import NO_DB_ALIAS
 from django.db.backends.postgresql_psycopg2.base import (
     DatabaseWrapper as Psycopg2DatabaseWrapper,
     DatabaseFeatures as Psycopg2DatabaseFeatures
@@ -31,7 +31,7 @@ class DatabaseWrapper(Psycopg2DatabaseWrapper):
     @cached_property
     def template_postgis(self):
         template_postgis = getattr(settings, 'POSTGIS_TEMPLATE', 'template_postgis')
-        with self.cursor() as cursor:
+        with self._nodb_connection.cursor() as cursor:
             cursor.execute('SELECT 1 FROM pg_database WHERE datname = %s LIMIT 1;', (template_postgis,))
             if cursor.fetchone():
                 return template_postgis
@@ -43,4 +43,3 @@ class DatabaseWrapper(Psycopg2DatabaseWrapper):
             # Check that postgis extension is installed on PostGIS >= 2
             with self.cursor() as cursor:
                 cursor.execute("CREATE EXTENSION IF NOT EXISTS postgis")
-                cursor.connection.commit()

django/contrib/gis/tests/geoapp/tests.py

@@ -2,7 +2,6 @@ from __future__ import unicode_literals
 
 import re
 from tempfile import NamedTemporaryFile
-import unittest
 
 from django.db import connection
 from django.contrib.gis import gdal
@@ -292,6 +291,11 @@ class GeoLookupTest(TestCase):
         # Right: A >> B => true if xmin(A) > xmax(B)
         # See: BOX2D_left() and BOX2D_right() in lwgeom_box2dfloat4.c in PostGIS source.
 
+        # The left/right lookup tests are known failures on PostGIS 2.0/2.0.1
+        # http://trac.osgeo.org/postgis/ticket/2035
+        if postgis_bug_version():
+            self.skipTest("PostGIS 2.0/2.0.1 left and right lookups are known to be buggy.")
+
         # Getting the borders for Colorado & Kansas
         co_border = State.objects.get(name='Colorado').poly
         ks_border = State.objects.get(name='Kansas').poly
@@ -325,11 +329,6 @@ class GeoLookupTest(TestCase):
         for c in qs:
             self.assertIn(c.name, cities)
 
-    # The left/right lookup tests are known failures on PostGIS 2.0/2.0.1
-    # http://trac.osgeo.org/postgis/ticket/2035
-    if postgis_bug_version():
-        test_left_right_lookups = unittest.expectedFailure(test_left_right_lookups)
-
     def test_equals_lookups(self):
         "Testing the 'same_as' and 'equals' lookup types."
         pnt = fromstr('POINT (-95.363151 29.763374)', srid=4326)

django/db/backends/__init__.py

@@ -30,6 +30,8 @@ TableInfo = namedtuple('TableInfo', ['name', 'type'])
 FieldInfo = namedtuple('FieldInfo',
     'name type_code display_size internal_size precision scale null_ok')
 
+NO_DB_ALIAS = '__no_db__'
+
 
 class BaseDatabaseWrapper(object):
     """
@@ -477,6 +479,24 @@ class BaseDatabaseWrapper(object):
             if must_close:
                 self.close()
 
+    @cached_property
+    def _nodb_connection(self):
+        """
+        Alternative connection to be used when there is no need to access
+        the main database, specifically for test db creation/deletion.
+        This also prevents the production database from being exposed to
+        potential child threads while (or after) the test database is destroyed.
+        Refs #10868, #17786, #16969.
+        """
+        settings_dict = self.settings_dict.copy()
+        settings_dict['NAME'] = None
+        #backend = load_backend(settings_dict['ENGINE'])
+        nodb_connection = self.__class__(
+            settings_dict,
+            alias=NO_DB_ALIAS,
+            allow_thread_sharing=False)
+        return nodb_connection
+
     def _start_transaction_under_autocommit(self):
         """
         Only required when autocommits_when_autocommit_is_off = True.

django/db/backends/creation.py

@@ -3,9 +3,7 @@ import sys
 import time
 
 from django.conf import settings
-from django.db.utils import load_backend
 from django.utils.encoding import force_bytes
-from django.utils.functional import cached_property
 from django.utils.six.moves import input
 from django.utils.six import StringIO
 from django.db import router
@@ -17,7 +15,6 @@ from .utils import truncate_name
 # The prefix to put on the default database name when creating
 # the test database.
 TEST_DATABASE_PREFIX = 'test_'
-NO_DB_ALIAS = '__no_db__'
 
 
 class BaseDatabaseCreation(object):
@@ -34,23 +31,12 @@ class BaseDatabaseCreation(object):
     def __init__(self, connection):
         self.connection = connection
 
-    @cached_property
+    @property
     def _nodb_connection(self):
         """
-        Alternative connection to be used when there is no need to access
-        the main database, specifically for test db creation/deletion.
-        This also prevents the production database from being exposed to
-        potential child threads while (or after) the test database is destroyed.
-        Refs #10868, #17786, #16969.
-        """
-        settings_dict = self.connection.settings_dict.copy()
-        settings_dict['NAME'] = None
-        backend = load_backend(settings_dict['ENGINE'])
-        nodb_connection = backend.DatabaseWrapper(
-            settings_dict,
-            alias=NO_DB_ALIAS,
-            allow_thread_sharing=False)
-        return nodb_connection
+        Used to be defined here, now moved to DatabaseWrapper.
+        """
+        return self.connection._nodb_connection
 
     @classmethod
     def _digest(cls, *args):