Truly test pymongo v2.8 instead of v2.9.

Testing v2.9 was unexpected and it's not as important given v2.9 mostly
mostly just provided an upgrade path for v3.0, and we already test v3.x.

.travis.yml

@@ -1,3 +1,6 @@
+# Use a container-based environment
+sudo: false
+
 language: python
 
 python:
@@ -8,26 +11,41 @@ python:
 - pypy
 - pypy3
 
+# Test on PyMongo v2.7.x, v2.8.x, and v3.x
 env:
 - PYMONGO=2.7
 - PYMONGO=2.8
 - PYMONGO=3.0
-- PYMONGO=dev
 
 matrix:
   fast_finish: true
 
-before_install:
+services:
-- travis_retry sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
+- mongodb
-- echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' |
+
-  sudo tee /etc/apt/sources.list.d/mongodb.list
+addons:
-- travis_retry sudo apt-get update
+  apt:
-- travis_retry sudo apt-get install mongodb-org-server
+    sources:
+    - mongodb-upstart
+    packages:
+    - mongodb-org-server=2.6.9
+
+    # Optional dependencies for the ImageField and others
+    - python-dev
+    - python3-dev
+    - libopenjpeg-dev
+    - zlib1g-dev
+    - libjpeg-turbo8-dev
+    - libtiff4-dev
+    - libjpeg8-dev
+    - libfreetype6-dev
+    - liblcms2-dev
+    - libwebp-dev
+    - tcl8.5-dev
+    - tk8.5-dev
+    - python-tk
 
 install:
-- sudo apt-get install python-dev python3-dev libopenjpeg-dev zlib1g-dev libjpeg-turbo8-dev
-  libtiff4-dev libjpeg8-dev libfreetype6-dev liblcms2-dev libwebp-dev tcl8.5-dev tk8.5-dev
-  python-tk
 - travis_retry pip install --upgrade pip
 - travis_retry pip install coveralls
 - travis_retry pip install flake8
@@ -35,6 +53,9 @@ install:
 - travis_retry pip install "virtualenv<14.0.0"  # virtualenv>=14.0.0 has dropped Python 3.2 support (and pypy3 is based on py32)
 - travis_retry tox -e $(echo py$TRAVIS_PYTHON_VERSION-mg$PYMONGO | tr -d . | sed -e 's/pypypy/pypy/') -- -e test
 
+# Cache dependencies installed via pip
+cache: pip
+
 # Run flake8 for py27
 before_script:
 - if [[ $TRAVIS_PYTHON_VERSION == '2.7' ]]; then tox -e flake8; fi
@@ -45,7 +66,7 @@ script:
 # For now only submit coveralls for Python v2.7. Python v3.x currently shows
 # 0% coverage. That's caused by 'use_2to3', which builds the py3-compatible
 # code in a separate dir and runs tests on that.
-after_script:
+after_success:
 - if [[ $TRAVIS_PYTHON_VERSION == '2.7' ]]; then coveralls --verbose; fi
 
 notifications:
@@ -56,11 +77,22 @@ branches:
   - master
   - /^v.*$/
 
+# Whenever a new release is created via GitHub, publish it on PyPI.
 deploy:
   provider: pypi
   user: the_drow
   password:
     secure: QMyatmWBnC6ZN3XLW2+fTBDU4LQcp1m/LjR2/0uamyeUzWKdlOoh/Wx5elOgLwt/8N9ppdPeG83ose1jOz69l5G0MUMjv8n/RIcMFSpCT59tGYqn3kh55b0cIZXFT9ar+5cxlif6a5rS72IHm5li7QQyxexJIII6Uxp0kpvUmek=
+
+  # create a source distribution and a pure python wheel for faster installs
+  distributions: "sdist bdist_wheel"
+
+  # only deploy on tagged commits (aka GitHub releases) and only for the
+  # parent repo's builds running Python 2.7 along with dev PyMongo (we run
+  # Travis against many different Python and PyMongo versions and we don't
+  # want the deploy to occur multiple times).
   on:
     tags: true
     repo: MongoEngine/mongoengine
+    condition: "$PYMONGO = 3.0"
+    python: 2.7

README.rst

@@ -35,16 +35,22 @@ setup.py install``.
 
 Dependencies
 ============
-- pymongo>=2.7.1
+All of the dependencies can easily be installed via `pip <https://pip.pypa.io/>`_. At the very least, you'll need these two packages to use MongoEngine:
-- sphinx (optional - for documentation generation)
+
+- pymongo>=2.7.1
+- six>=1.10.0
+
+If you utilize a ``DateTimeField``, you might also use a more flexible date parser:
 
-Optional Dependencies
----------------------
-- **Image Fields**: Pillow>=2.0.0
 - dateutil>=2.1.0
 
-.. note
+If you need to use an ``ImageField`` or ``ImageGridFsProxy``:
-   MongoEngine always runs it's test suite against the latest patch version of each dependecy. e.g.: PyMongo 3.0.1
+
+- Pillow>=2.0.0
+
+If you want to generate the documentation (e.g. to contribute to it):
+
+- sphinx
 
 Examples
 ========

docs/changelog.rst

@@ -5,6 +5,8 @@ Changelog
 Development
 ===========
 - (Fill this out as you fix issues and develop you features).
+- POTENTIAL BREAKING CHANGE: Fixed limit/skip/hint/batch_size chaining #1476
+- POTENTIAL BREAKING CHANGE: Changed a public `QuerySet.clone_into` method to a private `QuerySet._clone_into` #1476
 - Fixed connecting to a replica set with PyMongo 2.x #1436
 - Fixed an obscure error message when filtering by `field__in=non_iterable`. #1237
 

docs/guide/defining-documents.rst

@@ -361,11 +361,6 @@ Its value can take any of the following constants:
    In Django, be sure to put all apps that have such delete rule declarations in
    their :file:`models.py` in the :const:`INSTALLED_APPS` tuple.
 
-
-.. warning::
-   Signals are not triggered when doing cascading updates / deletes - if this
-   is required you must manually handle the update / delete.
-
 Generic reference fields
 ''''''''''''''''''''''''
 A second kind of reference field also exists,

docs/guide/signals.rst

@@ -142,11 +142,4 @@ cleaner looking while still allowing manual execution of the callback::
         modified = DateTimeField()
 
 
-ReferenceFields and Signals
----------------------------
-
-Currently `reverse_delete_rule` does not trigger signals on the other part of
-the relationship.  If this is required you must manually handle the
-reverse deletion.
-
 .. _blinker: http://pypi.python.org/pypi/blinker

docs/upgrade.rst

@@ -2,6 +2,20 @@
 Upgrading
 #########
 
+Development
+***********
+(Fill this out whenever you introduce breaking changes to MongoEngine)
+
+This release includes various fixes for the `BaseQuerySet` methods and how they
+are chained together. Since version 0.10.1 applying limit/skip/hint/batch_size
+to an already-existing queryset wouldn't modify the underlying PyMongo cursor.
+This has been fixed now, so you'll need to make sure that your code didn't rely
+on the broken implementation.
+
+Additionally, a public `BaseQuerySet.clone_into` has been renamed to a private
+`_clone_into`. If you directly used that method in your code, you'll need to
+rename its occurrences.
+
 0.11.0
 ******
 This release includes a major rehaul of MongoEngine's code quality and

mongoengine/fields.py

@@ -888,10 +888,6 @@ class ReferenceField(BaseField):
 
         Foo.register_delete_rule(Bar, 'foo', NULLIFY)
 
-    .. note ::
-        `reverse_delete_rule` does not trigger pre / post delete signals to be
-        triggered.
-
     .. versionchanged:: 0.5 added `reverse_delete_rule`
     """
 

mongoengine/queryset/base.py

@@ -86,6 +86,7 @@ class BaseQuerySet(object):
         self._batch_size = None
         self.only_fields = []
         self._max_time_ms = None
+        self._comment = None
 
     def __call__(self, q_obj=None, class_check=True, read_preference=None,
                  **query):
@@ -296,25 +297,22 @@ class BaseQuerySet(object):
             result = None
         return result
 
-    def insert(self, doc_or_docs, load_bulk=True, write_concern=None,
+    def insert(self, doc_or_docs, load_bulk=True,
-               signal_kwargs=None, continue_on_error=None):
+               write_concern=None, signal_kwargs=None):
         """bulk insert documents
 
         :param doc_or_docs: a document or list of documents to be inserted
         :param load_bulk (optional): If True returns the list of document
             instances
-        :param write_concern: Optional keyword argument passed down to
+        :param write_concern: Extra keyword arguments are passed down to
-                :meth:`~pymongo.collection.Collection.insert`, representing
+                :meth:`~pymongo.collection.Collection.insert`
-                the write concern. For example,
+                which will be used as options for the resultant
-                ``insert(..., write_concert={w: 2, fsync: True})`` will
+                ``getLastError`` command.  For example,
-                wait until at least two servers have recorded the write
+                ``insert(..., {w: 2, fsync: True})`` will wait until at least
-                and will force an fsync on each server being written to.
+                two servers have recorded the write and will force an fsync on
+                each server being written to.
         :parm signal_kwargs: (optional) kwargs dictionary to be passed to
             the signal calls.
-        :param continue_on_error: Optional keyword argument passed down to
-                :meth:`~pymongo.collection.Collection.insert`. Defines what
-                to do when a document cannot be inserted (e.g. due to
-                duplicate IDs). Read PyMongo's docs for more info.
 
         By default returns document instances, set ``load_bulk`` to False to
         return just ``ObjectIds``
@@ -325,10 +323,12 @@ class BaseQuerySet(object):
         """
         Document = _import_class('Document')
 
-        # Determine if we're inserting one doc or more
+        if write_concern is None:
+            write_concern = {}
+
         docs = doc_or_docs
         return_one = False
-        if isinstance(docs, Document):
+        if isinstance(docs, Document) or issubclass(docs.__class__, Document):
             return_one = True
             docs = [docs]
 
@@ -345,16 +345,9 @@ class BaseQuerySet(object):
         signals.pre_bulk_insert.send(self._document,
                                      documents=docs, **signal_kwargs)
 
-        # Resolve optional insert kwargs
-        insert_kwargs = {}
-        if write_concern is not None:
-            insert_kwargs.update(write_concern)
-        if continue_on_error is not None:
-            insert_kwargs['continue_on_error'] = continue_on_error
-
         raw = [doc.to_mongo() for doc in docs]
         try:
-            ids = self._collection.insert(raw, **insert_kwargs)
+            ids = self._collection.insert(raw, **write_concern)
         except pymongo.errors.DuplicateKeyError as err:
             message = 'Could not save document (%s)'
             raise NotUniqueError(message % six.text_type(err))
@@ -714,39 +707,36 @@ class BaseQuerySet(object):
         with switch_db(self._document, alias) as cls:
             collection = cls._get_collection()
 
-        return self.clone_into(self.__class__(self._document, collection))
+        return self._clone_into(self.__class__(self._document, collection))
 
     def clone(self):
-        """Creates a copy of the current
+        """Create a copy of the current queryset."""
-          :class:`~mongoengine.queryset.QuerySet`
+        return self._clone_into(self.__class__(self._document, self._collection_obj))
 
-        .. versionadded:: 0.5
+    def _clone_into(self, new_qs):
+        """Copy all of the relevant properties of this queryset to
+        a new queryset (which has to be an instance of
+        :class:`~mongoengine.queryset.base.BaseQuerySet`).
         """
-        return self.clone_into(self.__class__(self._document, self._collection_obj))
+        if not isinstance(new_qs, BaseQuerySet):
-
-    def clone_into(self, cls):
-        """Creates a copy of the current
-          :class:`~mongoengine.queryset.base.BaseQuerySet` into another child class
-        """
-        if not isinstance(cls, BaseQuerySet):
             raise OperationError(
-                '%s is not a subclass of BaseQuerySet' % cls.__name__)
+                '%s is not a subclass of BaseQuerySet' % new_qs.__name__)
 
         copy_props = ('_mongo_query', '_initial_query', '_none', '_query_obj',
                       '_where_clause', '_loaded_fields', '_ordering', '_snapshot',
                       '_timeout', '_class_check', '_slave_okay', '_read_preference',
                       '_iter', '_scalar', '_as_pymongo', '_as_pymongo_coerce',
                       '_limit', '_skip', '_hint', '_auto_dereference',
-                      '_search_text', 'only_fields', '_max_time_ms')
+                      '_search_text', 'only_fields', '_max_time_ms', '_comment')
 
         for prop in copy_props:
             val = getattr(self, prop)
-            setattr(cls, prop, copy.copy(val))
+            setattr(new_qs, prop, copy.copy(val))
 
         if self._cursor_obj:
-            cls._cursor_obj = self._cursor_obj.clone()
+            new_qs._cursor_obj = self._cursor_obj.clone()
 
-        return cls
+        return new_qs
 
     def select_related(self, max_depth=1):
         """Handles dereferencing of :class:`~bson.dbref.DBRef` objects or
@@ -768,7 +758,11 @@ class BaseQuerySet(object):
         """
         queryset = self.clone()
         queryset._limit = n if n != 0 else 1
-        # Return self to allow chaining
+
+        # If a cursor object has already been created, apply the limit to it.
+        if queryset._cursor_obj:
+            queryset._cursor_obj.limit(queryset._limit)
+
         return queryset
 
     def skip(self, n):
@@ -779,6 +773,11 @@ class BaseQuerySet(object):
         """
         queryset = self.clone()
         queryset._skip = n
+
+        # If a cursor object has already been created, apply the skip to it.
+        if queryset._cursor_obj:
+            queryset._cursor_obj.skip(queryset._skip)
+
         return queryset
 
     def hint(self, index=None):
@@ -796,6 +795,11 @@ class BaseQuerySet(object):
         """
         queryset = self.clone()
         queryset._hint = index
+
+        # If a cursor object has already been created, apply the hint to it.
+        if queryset._cursor_obj:
+            queryset._cursor_obj.hint(queryset._hint)
+
         return queryset
 
     def batch_size(self, size):
@@ -809,6 +813,11 @@ class BaseQuerySet(object):
         """
         queryset = self.clone()
         queryset._batch_size = size
+
+        # If a cursor object has already been created, apply the batch size to it.
+        if queryset._cursor_obj:
+            queryset._cursor_obj.batch_size(queryset._batch_size)
+
         return queryset
 
     def distinct(self, field):
@@ -980,13 +989,31 @@ class BaseQuerySet(object):
     def order_by(self, *keys):
         """Order the :class:`~mongoengine.queryset.QuerySet` by the keys. The
         order may be specified by prepending each of the keys by a + or a -.
-        Ascending order is assumed.
+        Ascending order is assumed. If no keys are passed, existing ordering
+        is cleared instead.
 
         :param keys: fields to order the query results by; keys may be
             prefixed with **+** or **-** to determine the ordering direction
         """
         queryset = self.clone()
-        queryset._ordering = queryset._get_order_by(keys)
+
+        old_ordering = queryset._ordering
+        new_ordering = queryset._get_order_by(keys)
+
+        if queryset._cursor_obj:
+
+            # If a cursor object has already been created, apply the sort to it
+            if new_ordering:
+                queryset._cursor_obj.sort(new_ordering)
+
+            # If we're trying to clear a previous explicit ordering, we need
+            # to clear the cursor entirely (because PyMongo doesn't allow
+            # clearing an existing sort on a cursor).
+            elif old_ordering:
+                queryset._cursor_obj = None
+
+        queryset._ordering = new_ordering
+
         return queryset
 
     def comment(self, text):
@@ -1432,10 +1459,13 @@ class BaseQuerySet(object):
             raise StopIteration
 
         raw_doc = self._cursor.next()
+
         if self._as_pymongo:
             return self._get_as_pymongo(raw_doc)
-        doc = self._document._from_son(raw_doc,
+
-                                       _auto_dereference=self._auto_dereference, only_fields=self.only_fields)
+        doc = self._document._from_son(
+            raw_doc, _auto_dereference=self._auto_dereference,
+            only_fields=self.only_fields)
 
         if self._scalar:
             return self._get_scalar(doc)
@@ -1445,7 +1475,6 @@ class BaseQuerySet(object):
     def rewind(self):
         """Rewind the cursor to its unevaluated state.
 
-
         .. versionadded:: 0.3
         """
         self._iter = False
@@ -1495,11 +1524,16 @@ class BaseQuerySet(object):
 
     @property
     def _cursor(self):
-        if self._cursor_obj is None:
+        """Return a PyMongo cursor object corresponding to this queryset."""
 
-            # In PyMongo 3+, we define the read preference on a collection
+        # If _cursor_obj already exists, return it immediately.
-            # level, not a cursor level. Thus, we need to get a cloned
+        if self._cursor_obj is not None:
-            # collection object using `with_options` first.
+            return self._cursor_obj
+
+        # Create a new PyMongo cursor.
+        # XXX In PyMongo 3+, we define the read preference on a collection
+        # level, not a cursor level. Thus, we need to get a cloned collection
+        # object using `with_options` first.
         if IS_PYMONGO_3 and self._read_preference is not None:
             self._cursor_obj = self._collection\
                 .with_options(read_preference=self._read_preference)\
@@ -1507,17 +1541,23 @@ class BaseQuerySet(object):
         else:
             self._cursor_obj = self._collection.find(self._query,
                                                      **self._cursor_args)
-            # Apply where clauses to cursor
+        # Apply "where" clauses to cursor
         if self._where_clause:
             where_clause = self._sub_js_fields(self._where_clause)
             self._cursor_obj.where(where_clause)
 
+        # Apply ordering to the cursor.
+        # XXX self._ordering can be equal to:
+        # * None if we didn't explicitly call order_by on this queryset.
+        # * A list of PyMongo-style sorting tuples.
+        # * An empty list if we explicitly called order_by() without any
+        #   arguments. This indicates that we want to clear the default
+        #   ordering.
         if self._ordering:
-                # Apply query ordering
+            # explicit ordering
             self._cursor_obj.sort(self._ordering)
         elif self._ordering is None and self._document._meta['ordering']:
-                # Otherwise, apply the ordering from the document model, unless
+            # default ordering
-                # it's been explicitly cleared via order_by with no arguments
             order = self._get_order_by(self._document._meta['ordering'])
             self._cursor_obj.sort(order)
 
@@ -1706,7 +1746,13 @@ class BaseQuerySet(object):
         return ret
 
     def _get_order_by(self, keys):
-        """Creates a list of order by fields"""
+        """Given a list of MongoEngine-style sort keys, return a list
+        of sorting tuples that can be applied to a PyMongo cursor. For
+        example:
+
+        >>> qs._get_order_by(['-last_name', 'first_name'])
+        [('last_name', -1), ('first_name', 1)]
+        """
         key_list = []
         for key in keys:
             if not key:
@@ -1719,17 +1765,19 @@ class BaseQuerySet(object):
             direction = pymongo.ASCENDING
             if key[0] == '-':
                 direction = pymongo.DESCENDING
+
             if key[0] in ('-', '+'):
                 key = key[1:]
+
             key = key.replace('__', '.')
             try:
                 key = self._document._translate_field_name(key)
             except Exception:
+                # TODO this exception should be more specific
                 pass
+
             key_list.append((key, direction))
 
-        if self._cursor_obj and key_list:
-            self._cursor_obj.sort(key_list)
         return key_list
 
     def _get_scalar(self, doc):
@@ -1827,10 +1875,21 @@ class BaseQuerySet(object):
         return code
 
     def _chainable_method(self, method_name, val):
+        """Call a particular method on the PyMongo cursor call a particular chainable method
+        with the provided value.
+        """
         queryset = self.clone()
-        method = getattr(queryset._cursor, method_name)
+
-        method(val)
+        # Get an existing cursor object or create a new one
+        cursor = queryset._cursor
+
+        # Find the requested method on the cursor and call it with the
+        # provided value
+        getattr(cursor, method_name)(val)
+
+        # Cache the value on the queryset._{method_name}
         setattr(queryset, '_' + method_name, val)
+
         return queryset
 
     # Deprecated

mongoengine/queryset/queryset.py

@@ -136,13 +136,15 @@ class QuerySet(BaseQuerySet):
         return self._len
 
     def no_cache(self):
-        """Convert to a non_caching queryset
+        """Convert to a non-caching queryset
 
         .. versionadded:: 0.8.3 Convert to non caching queryset
         """
         if self._result_cache is not None:
             raise OperationError('QuerySet already cached')
-        return self.clone_into(QuerySetNoCache(self._document, self._collection))
+
+        return self._clone_into(QuerySetNoCache(self._document,
+                                                self._collection))
 
 
 class QuerySetNoCache(BaseQuerySet):
@@ -153,7 +155,7 @@ class QuerySetNoCache(BaseQuerySet):
 
         .. versionadded:: 0.8.3 Convert to caching queryset
         """
-        return self.clone_into(QuerySet(self._document, self._collection))
+        return self._clone_into(QuerySet(self._document, self._collection))
 
     def __repr__(self):
         """Provides the string representation of the QuerySet

tests/queryset/queryset.py

@@ -106,58 +106,111 @@ class QuerySetTest(unittest.TestCase):
             list(BlogPost.objects(author2__name="test"))
 
     def test_find(self):
-        """Ensure that a query returns a valid set of results.
+        """Ensure that a query returns a valid set of results."""
-        """
+        user_a = self.Person.objects.create(name='User A', age=20)
-        self.Person(name="User A", age=20).save()
+        user_b = self.Person.objects.create(name='User B', age=30)
-        self.Person(name="User B", age=30).save()
 
         # Find all people in the collection
         people = self.Person.objects
         self.assertEqual(people.count(), 2)
         results = list(people)
+
         self.assertTrue(isinstance(results[0], self.Person))
         self.assertTrue(isinstance(results[0].id, (ObjectId, str, unicode)))
-        self.assertEqual(results[0].name, "User A")
+
+        self.assertEqual(results[0], user_a)
+        self.assertEqual(results[0].name, 'User A')
         self.assertEqual(results[0].age, 20)
-        self.assertEqual(results[1].name, "User B")
+
+        self.assertEqual(results[1], user_b)
+        self.assertEqual(results[1].name, 'User B')
         self.assertEqual(results[1].age, 30)
 
-        # Use a query to filter the people found to just person1
+        # Filter people by age
         people = self.Person.objects(age=20)
         self.assertEqual(people.count(), 1)
         person = people.next()
+        self.assertEqual(person, user_a)
         self.assertEqual(person.name, "User A")
         self.assertEqual(person.age, 20)
 
-        # Test limit
+    def test_limit(self):
+        """Ensure that QuerySet.limit works as expected."""
+        user_a = self.Person.objects.create(name='User A', age=20)
+        user_b = self.Person.objects.create(name='User B', age=30)
+
+        # Test limit on a new queryset
         people = list(self.Person.objects.limit(1))
         self.assertEqual(len(people), 1)
-        self.assertEqual(people[0].name, 'User A')
+        self.assertEqual(people[0], user_a)
 
-        # Test skip
+        # Test limit on an existing queryset
+        people = self.Person.objects
+        self.assertEqual(len(people), 2)
+        people2 = people.limit(1)
+        self.assertEqual(len(people), 2)
+        self.assertEqual(len(people2), 1)
+        self.assertEqual(people2[0], user_a)
+
+        # Test chaining of only after limit
+        person = self.Person.objects().limit(1).only('name').first()
+        self.assertEqual(person, user_a)
+        self.assertEqual(person.name, 'User A')
+        self.assertEqual(person.age, None)
+
+    def test_skip(self):
+        """Ensure that QuerySet.skip works as expected."""
+        user_a = self.Person.objects.create(name='User A', age=20)
+        user_b = self.Person.objects.create(name='User B', age=30)
+
+        # Test skip on a new queryset
         people = list(self.Person.objects.skip(1))
         self.assertEqual(len(people), 1)
-        self.assertEqual(people[0].name, 'User B')
+        self.assertEqual(people[0], user_b)
 
-        person3 = self.Person(name="User C", age=40)
+        # Test skip on an existing queryset
-        person3.save()
+        people = self.Person.objects
+        self.assertEqual(len(people), 2)
+        people2 = people.skip(1)
+        self.assertEqual(len(people), 2)
+        self.assertEqual(len(people2), 1)
+        self.assertEqual(people2[0], user_b)
+
+        # Test chaining of only after skip
+        person = self.Person.objects().skip(1).only('name').first()
+        self.assertEqual(person, user_b)
+        self.assertEqual(person.name, 'User B')
+        self.assertEqual(person.age, None)
+
+    def test_slice(self):
+        """Ensure slicing a queryset works as expected."""
+        user_a = self.Person.objects.create(name='User A', age=20)
+        user_b = self.Person.objects.create(name='User B', age=30)
+        user_c = self.Person.objects.create(name="User C", age=40)
 
         # Test slice limit
         people = list(self.Person.objects[:2])
         self.assertEqual(len(people), 2)
-        self.assertEqual(people[0].name, 'User A')
+        self.assertEqual(people[0], user_a)
-        self.assertEqual(people[1].name, 'User B')
+        self.assertEqual(people[1], user_b)
 
         # Test slice skip
         people = list(self.Person.objects[1:])
         self.assertEqual(len(people), 2)
-        self.assertEqual(people[0].name, 'User B')
+        self.assertEqual(people[0], user_b)
-        self.assertEqual(people[1].name, 'User C')
+        self.assertEqual(people[1], user_c)
 
         # Test slice limit and skip
         people = list(self.Person.objects[1:2])
         self.assertEqual(len(people), 1)
-        self.assertEqual(people[0].name, 'User B')
+        self.assertEqual(people[0], user_b)
+
+        # Test slice limit and skip on an existing queryset
+        people = self.Person.objects
+        self.assertEqual(len(people), 3)
+        people2 = people[1:2]
+        self.assertEqual(len(people2), 1)
+        self.assertEqual(people2[0], user_b)
 
         # Test slice limit and skip cursor reset
         qs = self.Person.objects[1:2]
@@ -168,6 +221,7 @@ class QuerySetTest(unittest.TestCase):
         self.assertEqual(len(people), 1)
         self.assertEqual(people[0].name, 'User B')
 
+        # Test empty slice
         people = list(self.Person.objects[1:1])
         self.assertEqual(len(people), 0)
 
@@ -187,12 +241,6 @@ class QuerySetTest(unittest.TestCase):
         self.assertEqual("[<Person: Person object>, <Person: Person object>]",
                          "%s" % self.Person.objects[51:53])
 
-        # Test only after limit
-        self.assertEqual(self.Person.objects().limit(2).only('name')[0].age, None)
-
-        # Test only after skip
-        self.assertEqual(self.Person.objects().skip(2).only('name')[0].age, None)
-
     def test_find_one(self):
         """Ensure that a query using find_one returns a valid result.
         """
@@ -766,7 +814,8 @@ class QuerySetTest(unittest.TestCase):
         self.assertEqual(record.embed.field, 2)
 
     def test_bulk_insert(self):
-        """Ensure that bulk insert works."""
+        """Ensure that bulk insert works
+        """
 
         class Comment(EmbeddedDocument):
             name = StringField()
@@ -884,37 +933,9 @@ class QuerySetTest(unittest.TestCase):
 
         self.assertEqual(Blog.objects.count(), 2)
 
-    def test_bulk_insert_continue_on_error(self):
+        Blog.objects.insert([blog2, blog3],
-        """Ensure that bulk insert works with the continue_on_error option."""
+                            write_concern={"w": 0, 'continue_on_error': True})
-
+        self.assertEqual(Blog.objects.count(), 3)
-        class Person(Document):
-            email = EmailField(unique=True)
-
-        Person.drop_collection()
-
-        Person.objects.insert([
-            Person(email='alice@example.com'),
-            Person(email='bob@example.com')
-        ])
-        self.assertEqual(Person.objects.count(), 2)
-
-        new_docs = [
-            Person(email='alice@example.com'),  # dupe
-            Person(email='bob@example.com'),  # dupe
-            Person(email='steve@example.com')  # new one
-        ]
-
-        # By default inserting dupe docs should fail and no new docs should
-        # be inserted.
-        with self.assertRaises(NotUniqueError):
-            Person.objects.insert(new_docs)
-        self.assertEqual(Person.objects.count(), 2)
-
-        # With continue_on_error, new doc should be inserted, even though we
-        # still get a NotUniqueError caused by the other 2 dupes.
-        with self.assertRaises(NotUniqueError):
-            Person.objects.insert(new_docs, continue_on_error=True)
-        self.assertEqual(Person.objects.count(), 3)
 
     def test_get_changed_fields_query_count(self):
 
@@ -1253,6 +1274,7 @@ class QuerySetTest(unittest.TestCase):
 
         BlogPost.drop_collection()
 
+        # default ordering should be used by default
         with db_ops_tracker() as q:
             BlogPost.objects.filter(title='whatever').first()
             self.assertEqual(len(q.get_ops()), 1)
@@ -1261,11 +1283,28 @@ class QuerySetTest(unittest.TestCase):
                 {'published_date': -1}
             )
 
+        # calling order_by() should clear the default ordering
         with db_ops_tracker() as q:
             BlogPost.objects.filter(title='whatever').order_by().first()
             self.assertEqual(len(q.get_ops()), 1)
             self.assertFalse('$orderby' in q.get_ops()[0]['query'])
 
+        # calling an explicit order_by should use a specified sort
+        with db_ops_tracker() as q:
+            BlogPost.objects.filter(title='whatever').order_by('published_date').first()
+            self.assertEqual(len(q.get_ops()), 1)
+            self.assertEqual(
+                q.get_ops()[0]['query']['$orderby'],
+                {'published_date': 1}
+            )
+
+        # calling order_by() after an explicit sort should clear it
+        with db_ops_tracker() as q:
+            qs = BlogPost.objects.filter(title='whatever').order_by('published_date')
+            qs.order_by().first()
+            self.assertEqual(len(q.get_ops()), 1)
+            self.assertFalse('$orderby' in q.get_ops()[0]['query'])
+
     def test_no_ordering_for_get(self):
         """ Ensure that Doc.objects.get doesn't use any ordering.
         """

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = {py26,py27,py33,py34,py35,pypy,pypy3}-{mg27,mg28},flake8
+envlist = {py27,py33,py34,py35,pypy,pypy3}-{mg27,mg28,mg30},flake8
 
 [testenv]
 commands =
@@ -7,12 +7,10 @@ commands =
 deps =
     nose
     mg27: PyMongo<2.8
-    mg28: PyMongo>=2.8,<3.0
+    mg28: PyMongo>=2.8,<2.9
     mg30: PyMongo>=3.0
-    mgdev: https://github.com/mongodb/mongo-python-driver/tarball/master
 setenv =
     PYTHON_EGG_CACHE = {envdir}/python-eggs
-passenv = windir
 
 [testenv:flake8]
 deps =