Improve connect/disconnect

- document disconnect + sample of usage
- add more test cases to prevent github issues regressions

docs/changelog.rst

@@ -5,7 +5,7 @@ Changelog
 Development
 ===========
 - expose `mongoengine.connection.disconnect` and `mongoengine.connection.disconnect_all`
-- POTENTIAL BREAKING CHANGE: Fixes in connect/disconnect methods
+- POTENTIAL BREAKING CHANGE: Fixes in connect/disconnect methods #565 #566
     - 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`
     - disconnect now clears the cached attribute `Document._collection`

docs/guide/connecting.rst

@@ -4,9 +4,11 @@
 Connecting to MongoDB
 =====================
 
-To connect to a running instance of :program:`mongod`, use the
+Connections in MongoEngine are registered globally and are identified with aliases.
-:func:`~mongoengine.connect` function. The first argument is the name of the
+If no `alias` is provided during the connection, it will use "default" as alias.
-database to connect to::
+
+To connect to a running instance of :program:`mongod`, use the :func:`~mongoengine.connect`
+function. The first argument is the name of the database to connect to::
 
     from mongoengine import connect
     connect('project1')
@@ -42,6 +44,9 @@ the :attr:`host` to
     will establish connection to ``production`` database using
     ``admin`` username and ``qwerty`` password.
 
+.. note:: Calling :func:`~mongoengine.connect` without argument will establish
+    a connection to the "test" database by default
+
 Replica Sets
 ============
 
@@ -71,6 +76,8 @@ is used.
 In the background this uses :func:`~mongoengine.register_connection` to
 store the data and you can register all aliases up front if required.
 
+Documents defined in different database
+---------------------------------------
 Individual documents can also support multiple databases by providing a
 `db_alias` in their meta data. This allows :class:`~pymongo.dbref.DBRef`
 objects to point across databases and collections. Below is an example schema,
@@ -93,6 +100,33 @@ using 3 different databases to store data::
             meta = {'db_alias': 'users-books-db'}
 
 
+Disconnecting an existing connection
+------------------------------------
+The function :func:`~mongoengine.disconnect` can be used to
+disconnect a particular connection. This can be used to change a
+connection globally::
+
+        from mongoengine import connect, disconnect
+        connect('a_db', alias='db1')
+
+        class User(Document):
+            name = StringField()
+            meta = {'db_alias': 'db1'}
+
+        disconnect(alias='db1')
+
+        connect('another_db', alias='db1')
+
+.. note:: Calling :func:`~mongoengine.disconnect` without argument
+    will disconnect the "default" connection
+
+.. note:: Since connections gets registered globally, it is important
+    to use the `disconnect` function from MongoEngine and not the
+    `disconnect()` method of an existing connection (pymongo.MongoClient)
+
+.. note:: :class:`~mongoengine.Document` are caching the pymongo collection.
+    using `disconnect` ensures that it gets cleaned as well
+
 Context Managers
 ================
 Sometimes you may want to switch the database or collection to query against.
@@ -119,7 +153,7 @@ access to the same User document across databases::
 
 Switch Collection
 -----------------
-The :class:`~mongoengine.context_managers.switch_collection` context manager
+The :func:`~mongoengine.context_managers.switch_collection` context manager
 allows you to change the collection for a given class allowing quick and easy
 access to the same Group document across collection::
 

mongoengine/connection.py

@@ -318,6 +318,9 @@ def connect(db=None, alias=DEFAULT_CONNECTION_NAME, **kwargs):
     Multiple databases are supported by using aliases. Provide a separate
     `alias` to connect to a different instance of :program:`mongod`.
 
+    In order to replace a connection identified by a given alias, you'll
+    need to call ``disconnect`` first
+
     See the docstring for `register_connection` for more details about all
     supported kwargs.
 

mongoengine/document.py

@@ -795,13 +795,13 @@ class Document(six.with_metaclass(TopLevelDocumentMetaclass, BaseDocument)):
         .. versionchanged:: 0.10.7
             :class:`OperationError` exception raised if no collection available
         """
-        col_name = cls._get_collection_name()
+        coll_name = cls._get_collection_name()
-        if not col_name:
+        if not coll_name:
             raise OperationError('Document %s has no collection defined '
                                  '(is it abstract ?)' % cls)
         cls._collection = None
         db = cls._get_db()
-        db.drop_collection(col_name)
+        db.drop_collection(coll_name)
 
     @classmethod
     def create_index(cls, keys, background=False, **kwargs):

tests/test_connection.py

@@ -1,4 +1,6 @@
 import datetime
+
+from pymongo import MongoClient
 from pymongo.errors import OperationFailure
 
 try:
@@ -238,12 +240,25 @@ class ConnectionTest(unittest.TestCase):
         conn = get_connection('testdb6')
         self.assertIsInstance(conn, mongomock.MongoClient)
 
-    def test_disconnect(self):
+    def test_disconnect_cleans_globals(self):
-        """Ensure that the disconnect() method works properly"""
+        """Ensure that the disconnect() method cleans the globals objects"""
         connections = mongoengine.connection._connections
         dbs = mongoengine.connection._dbs
         connection_settings = mongoengine.connection._connection_settings
 
+        connect('mongoenginetest')
+
+        self.assertEqual(len(connections), 1)
+        self.assertEqual(len(dbs), 1)
+        self.assertEqual(len(connection_settings), 1)
+
+        disconnect()
+        self.assertEqual(len(connections), 0)
+        self.assertEqual(len(dbs), 0)
+        self.assertEqual(len(connection_settings), 0)
+
+    def test_disconnect_cleans_cached_collection_attribute_in_document(self):
+        """Ensure that the disconnect() method works properly"""
         conn1 = connect('mongoenginetest')
 
         class History(Document):
@@ -252,29 +267,50 @@ class ConnectionTest(unittest.TestCase):
         self.assertIsNone(History._collection)
 
         History.drop_collection()
+
         History.objects.first()     # will trigger the caching of _collection attribute
-
         self.assertIsNotNone(History._collection)
 
-        self.assertEqual(len(connections), 1)
-        self.assertEqual(len(dbs), 1)
-        self.assertEqual(len(connection_settings), 1)
-
         disconnect()
 
         self.assertIsNone(History._collection)
 
-        self.assertEqual(len(connections), 0)
-        self.assertEqual(len(dbs), 0)
-        self.assertEqual(len(connection_settings), 0)
-
         with self.assertRaises(MongoEngineConnectionError) as ctx_err:
             History.objects.first()
         self.assertEqual("You have not defined a default connection", str(ctx_err.exception))
 
-        conn2 = connect('mongoenginetest')
+    def test_connect_disconnect_works_on_same_document(self):
-        History.objects.first()     # Make sure its back on track
+        """Ensure that the connect/disconnect works properly with a single Document"""
-        self.assertTrue(conn1 is not conn2)
+        db1 = 'db1'
+        db2 = 'db2'
+
+        # Ensure freshness of the 2 databases through pymongo
+        client = MongoClient('localhost', 27017)
+        client.drop_database(db1)
+        client.drop_database(db2)
+
+        # Save in db1
+        connect(db1)
+
+        class User(Document):
+            name = StringField(required=True)
+
+        user1 = User(name='John is in db1').save()
+        disconnect()
+
+        # Make sure save doesnt work at this stage
+        with self.assertRaises(MongoEngineConnectionError):
+            User(name='Wont work').save()
+
+        # Save in db2
+        connect(db2)
+        user2 = User(name='Bob is in db2').save()
+        disconnect()
+
+        db1_users = list(client[db1].user.find())
+        self.assertEqual(db1_users, [{'_id': user1.id, 'name': 'John is in db1'}])
+        db2_users = list(client[db2].user.find())
+        self.assertEqual(db2_users, [{'_id': user2.id, 'name': 'Bob is in db2'}])
 
     def test_disconnect_silently_pass_if_alias_does_not_exist(self):
         connections = mongoengine.connection._connections