Fixed postgis test database initialization

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

2 files changed, 23 insertions, 17 deletions

diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index ffe42e925d..bdf841cbd9 100644
--- a/django/db/backends/__init__.py
+++ b/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.
diff --git a/django/db/backends/creation.py b/django/db/backends/creation.py
index 18168deaca..d3def4ebe2 100644
--- a/django/db/backends/creation.py
+++ b/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.
+        Used to be defined here, now moved to DatabaseWrapper.
         """
-        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
+        return self.connection._nodb_connection
 
     @classmethod
     def _digest(cls, *args):