Removed try-except in django.db.close_connection()

The reason was that the except clause needed to remove a connection
from the django.db.connections dict, but other parts of Django do not
expect this to happen. In addition the except clause was silently
swallowing the exception messages.

Refs #19707, special thanks to Carl Meyer for pointing out that this
approach should be taken.

django/db/__init__.py

@@ -45,14 +45,11 @@ def close_connection(**kwargs):
     # Avoid circular imports
     from django.db import transaction
     for conn in connections:
-        try:
+        # If an error happens here the connection will be left in broken
+        # state. Once a good db connection is again available, the
+        # connection state will be cleaned up.
         transaction.abort(conn)
         connections[conn].close()
-        except Exception:
-            # The connection's state is unknown, so it has to be
-            # abandoned. This could happen for example if the network
-            # connection has a failure.
-            del connections[conn]
 signals.request_finished.connect(close_connection)
 
 # Register an event that resets connection.queries

django/db/utils.py

@@ -99,9 +99,6 @@ class ConnectionHandler(object):
     def __setitem__(self, key, value):
         setattr(self._connections, key, value)
 
-    def __delitem__(self, key):
-        delattr(self._connections, key)
-
     def __iter__(self):
         return iter(self.databases)
 

tests/regressiontests/requests/tests.py

@@ -548,9 +548,6 @@ class TransactionRequestTests(TransactionTestCase):
                      'This test will close the connection, in-memory '
                      'sqlite connections must not be closed.')
     def test_request_finished_failed_connection(self):
-        # See comments in test_request_finished_db_state() for the self.client
-        # usage.
-        response = self.client.get('/')
         conn = connections[DEFAULT_DB_ALIAS]
         conn.enter_transaction_management()
         conn.managed(True)
@@ -560,9 +557,14 @@ class TransactionRequestTests(TransactionTestCase):
         def fail_horribly():
             raise Exception("Horrible failure!")
         conn._rollback = fail_horribly
-        signals.request_finished.send(sender=response._handler_class)
-        # As even rollback wasn't possible the connection wrapper itself was
-        # abandoned. Accessing the connections[alias] will create a new
-        # connection wrapper, whch must be different than the original one.
-        self.assertIsNot(conn, connections[DEFAULT_DB_ALIAS])
+        try:
+            with self.assertRaises(Exception):
+                signals.request_finished.send(sender=self.__class__)
+            # The connection's state wasn't cleaned up
+            self.assertTrue(len(connection.transaction_state), 1)
+        finally:
+            del conn._rollback
+        # The connection will be cleaned on next request where the conn
+        # works again.
+        signals.request_finished.send(sender=self.__class__)
         self.assertEqual(len(connection.transaction_state), 0)