[multi-db] For all backends: commit only when a connection exists.

git-svn-id: http://code.djangoproject.com/svn/django/branches/multiple-db-support@4127 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/ado_mssql/base.py

@@ -70,6 +70,7 @@ class DatabaseWrapper(object):
         return cursor
 
     def _commit(self):
+        if self.connection:
             return self.connection.commit()
 
     def _rollback(self):

django/db/backends/mysql/base.py

@@ -91,6 +91,7 @@ class DatabaseWrapper(object):
         return cursor
 
     def _commit(self):
+        if self.connection:
             self.connection.commit()
 
     def _rollback(self):

django/db/backends/oracle/base.py

@@ -36,6 +36,7 @@ class DatabaseWrapper(object):
         return FormatStylePlaceholderCursor(self.connection)
 
     def _commit(self):
+        if self.connection:
             self.connection.commit()
 
     def _rollback(self):

django/db/backends/postgresql/base.py

@@ -43,6 +43,7 @@ class DatabaseWrapper(object):
         return cursor
 
     def _commit(self):
+        if self.connection:
             return self.connection.commit()
 
     def _rollback(self):

django/db/backends/postgresql_psycopg2/base.py

@@ -44,6 +44,7 @@ class DatabaseWrapper(object):
         return cursor
 
     def _commit(self):
+        if self.connection:
             return self.connection.commit()
 
     def _rollback(self):

django/db/backends/sqlite3/base.py

@@ -56,6 +56,7 @@ class DatabaseWrapper(local):
             return cursor
 
     def _commit(self):
+        if self.connection:
             self.connection.commit()
 
     def _rollback(self):