# 4.2. Changes in 0.19.1
Requires Pillow < 7.0.0 as it dropped Python2 support
DEPRECATION: The interface of QuerySet.aggregate method was changed, it no longer takes an unpacked list of
pipeline steps (*pipeline) but simply takes the pipeline list just like pymongo.Collection.aggregate does. #2079
# 4.3. Changes in 0.19.0
BREAKING CHANGE: class_check and read_preference keyword arguments are no longer available when filtering a QuerySet. #2112
Instead of Doc.objects(foo=bar, read_preference=...) use Doc.objects(foo=bar).read_preference(...).
Instead of Doc.objects(foo=bar, class_check=False) use Doc.objects(foo=bar).clear_cls_query(...).
This change also renames the private QuerySet._initial_query attribute to _cls_query.
BREAKING CHANGE: Removed the deprecated format param from QuerySet.explain. #2113
BREAKING CHANGE: Renamed MongoEngineConnectionError to ConnectionFailure. #2111
If you catch/use MongoEngineConnectionError in your code, you’ll have to rename it.
BREAKING CHANGE: Positional arguments when instantiating a document are no longer supported. #2103
From now on keyword arguments (e.g. Doc(field_name=value)) are required.
BREAKING CHANGE: A LazyReferenceField is now stored in the _data field of its parent as a DBRef, Document, or EmbeddedDocument (ObjectId is no longer allowed). #2182
DEPRECATION: Q.empty & QNode.empty are marked as deprecated and will be removed in a next version of MongoEngine. #2210
Added ability to check if Q or QNode are empty by parsing them to bool.
Instead of Q(name="John").empty use not Q(name="John").
Fix updating/modifying/deleting/reloading a document that’s sharded by a field with db_field specified. #2125
Only set no_cursor_timeout when requested (fixes an incompatibility with MongoDB 4.2) #2148
ListField now accepts an optional max_length parameter. #2110
Improve error message related to InvalidDocumentError #2180
Added BulkWriteError to replace NotUniqueError which was misleading in bulk write insert #2152
Added ability to compare Q and Q operations #2204
Added ability to use a db alias on query_counter #2194
Added ability to specify collations for querysets with Doc.objects.collation #2024
Fix updates of a list field by negative index #2094
Switch from nosetest to pytest as test runner #2114
The codebase is now formatted using black. #2109
Documentation improvements:
Documented how pymongo.monitoring can be used to log all queries issued by MongoEngine to the driver.