Fix connection issue when using different authentication in different dbs

docs/changelog.rst

@@ -13,6 +13,7 @@ Development
 - expose `mongoengine.connection.disconnect` and `mongoengine.connection.disconnect_all`
 - Fix disconnect function #566 #1599 #605 #607 #1213 #565
 - Improve connect/disconnect documentations
+- Fix issue when using multiple connections to the same mongo with different credentials #2047
 - POTENTIAL BREAKING CHANGES: (associated with connect/disconnect fixes)
     - calling `connect` 2 times with the same alias and different parameter will raise an error (should call disconnect first)
     - disconnect now clears `mongoengine.connection._connection_settings`

mongoengine/connection.py

@@ -235,7 +235,6 @@ def get_connection(alias=DEFAULT_CONNECTION_NAME, reconnect=False):
         raise MongoEngineConnectionError(msg)
 
     def _clean_settings(settings_dict):
-        # set literal more efficient than calling set function
         irrelevant_fields_set = {
             'name', 'username', 'password',
             'authentication_source', 'authentication_mechanism'
@@ -245,10 +244,12 @@ def _clean_settings(settings_dict):
             if k not in irrelevant_fields_set
         }
 
+    raw_conn_settings = _connection_settings[alias].copy()
+
     # Retrieve a copy of the connection settings associated with the requested
     # alias and remove the database name and authentication info (we don't
     # care about them at this point).
-    conn_settings = _clean_settings(_connection_settings[alias].copy())
+    conn_settings = _clean_settings(raw_conn_settings)
 
     # Determine if we should use PyMongo's or mongomock's MongoClient.
     is_mock = conn_settings.pop('is_mock', False)
@@ -262,35 +263,60 @@ def _clean_settings(settings_dict):
     else:
         connection_class = MongoClient
 
-    # Iterate over all of the connection settings and if a connection with
-    # the same parameters is already established, use it instead of creating
-    # a new one.
-    existing_connection = None
-    connection_settings_iterator = (
-        (db_alias, settings.copy())
-        for db_alias, settings in _connection_settings.items()
-    )
-    for db_alias, connection_settings in connection_settings_iterator:
-        connection_settings = _clean_settings(connection_settings)
-        if conn_settings == connection_settings and _connections.get(db_alias):
-            existing_connection = _connections[db_alias]
-            break
+    # Re-use existing connection if one is suitable
+    existing_connection = _find_existing_connection(raw_conn_settings)
 
     # If an existing connection was found, assign it to the new alias
     if existing_connection:
         _connections[alias] = existing_connection
     else:
-        # Otherwise, create the new connection for this alias. Raise
-        # MongoEngineConnectionError if it can't be established.
-        try:
-            _connections[alias] = connection_class(**conn_settings)
-        except Exception as e:
-            raise MongoEngineConnectionError(
-                'Cannot connect to database %s :\n%s' % (alias, e))
+        _connections[alias] = _create_connection(alias=alias,
+                                                 connection_class=connection_class,
+                                                 **conn_settings)
 
     return _connections[alias]
 
 
+def _create_connection(alias, connection_class, **connection_settings):
+    """
+    Create the new connection for this alias. Raise
+    MongoEngineConnectionError if it can't be established.
+    """
+    try:
+        return connection_class(**connection_settings)
+    except Exception as e:
+        raise MongoEngineConnectionError(
+            'Cannot connect to database %s :\n%s' % (alias, e))
+
+
+def _find_existing_connection(connection_settings):
+    """
+    Check if an existing connection could be reused
+
+    Iterate over all of the connection settings and if an existing connection
+    with the same parameters is suitable, return it
+
+    :param connection_settings: the settings of the new connection
+    :return: An existing connection or None
+    """
+    connection_settings_bis = (
+        (db_alias, settings.copy())
+        for db_alias, settings in _connection_settings.items()
+    )
+
+    def _clean_settings(settings_dict):
+        # Only remove the name but it's important to
+        # keep the username/password/authentication_source/authentication_mechanism
+        # to identify if the connection could be shared (cfr https://github.com/MongoEngine/mongoengine/issues/2047)
+        return {k: v for k, v in settings_dict.items() if k != 'name'}
+
+    cleaned_conn_settings = _clean_settings(connection_settings)
+    for db_alias, connection_settings in connection_settings_bis:
+        db_conn_settings = _clean_settings(connection_settings)
+        if cleaned_conn_settings == db_conn_settings and _connections.get(db_alias):
+            return _connections[db_alias]
+
+
 def get_db(alias=DEFAULT_CONNECTION_NAME, reconnect=False):
     if reconnect:
         disconnect(alias)

tests/test_connection.py

@@ -611,6 +611,16 @@ def test_multiple_connection_settings(self):
         self.assertEqual(mongo_connections['t1'].address[0], 'localhost')
         self.assertEqual(mongo_connections['t2'].address[0], '127.0.0.1')
 
+    def test_connect_2_databases_uses_same_client_if_only_dbname_differs(self):
+        c1 = connect(alias='testdb1', db='testdb1')
+        c2 = connect(alias='testdb2', db='testdb2')
+        self.assertIs(c1, c2)
+
+    def test_connect_2_databases_uses_different_client_if_different_parameters(self):
+        c1 = connect(alias='testdb1', db='testdb1', username='u1')
+        c2 = connect(alias='testdb2', db='testdb2', username='u2')
+        self.assertIsNot(c1, c2)
+
 
 if __name__ == '__main__':
     unittest.main()