[1.5.x] Fixed #18575 -- Empty DATABASES should default to dummy backend

Thanks delormemarco@gmail.com for the report.

Backport of f1cc2be from master.

django/conf/global_settings.py

@@ -150,12 +150,8 @@
 # Whether to send broken-link emails.
 SEND_BROKEN_LINK_EMAILS = False
 
-# Database connection info.
-DATABASES = {
-    'default': {
-        'ENGINE': 'django.db.backends.dummy',
-    },
-}
+# Database connection info. If left empty, will default to the dummy backend.
+DATABASES = {}
 
 # Classes used to implement DB routing behavior.
 DATABASE_ROUTERS = []

django/db/__init__.py

@@ -8,7 +8,7 @@
     'IntegrityError', 'DEFAULT_DB_ALIAS')
 
 
-if DEFAULT_DB_ALIAS not in settings.DATABASES:
+if settings.DATABASES and DEFAULT_DB_ALIAS not in settings.DATABASES:
     raise ImproperlyConfigured("You must define a '%s' database" % DEFAULT_DB_ALIAS)
 
 connections = ConnectionHandler(settings.DATABASES)

django/db/utils.py

@@ -53,7 +53,14 @@ class ConnectionDoesNotExist(Exception):
 
 class ConnectionHandler(object):
     def __init__(self, databases):
-        self.databases = databases
+        if not databases:
+            self.databases = {
+                DEFAULT_DB_ALIAS: {
+                    'ENGINE': 'django.db.backends.dummy',
+                },
+            }
+        else:
+            self.databases = databases
         self._connections = local()
 
     def ensure_defaults(self, alias):

tests/regressiontests/backends/tests.py

@@ -23,6 +23,17 @@
 from . import models
 
 
+class DummyBackendTest(TestCase):
+    def test_no_databases(self):
+        """
+        Test that empty DATABASES setting default to the dummy backend.
+        """
+        DATABASES = {}
+        conns = ConnectionHandler(DATABASES)
+        self.assertEqual(conns[DEFAULT_DB_ALIAS].settings_dict['ENGINE'],
+            'django.db.backends.dummy')
+
+
 class OracleChecks(unittest.TestCase):
 
     @unittest.skipUnless(connection.vendor == 'oracle',