Mongoengine

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- Declare that Py3.5 is not supported in package metadata 2449
- Moved CI from Travis to Github-Actions

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- Fix LazyReferenceField dereferencing in embedded documents 2426
- Fix regarding the recent use of Cursor.__spec in .count() that was interfering with mongomock 2425
- Drop support for Python 3.5 by introducing f-strings in the codebase

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- Bug fix in DynamicDocument which is not parsing known fields in constructor like Document do 2412
- When using pymongo >= 3.7, make use of Collection.count_documents instead of Collection.count
and Cursor.count that got deprecated in pymongo >= 3.7.
This should have a negative impact on performance of count see Issue 2219
- Fix a bug that made the queryset drop the read_preference after clone().
- Remove Py3.5 from CI as it reached EOL and add Python 3.9
- Fix some issues related with db_field/field conflict in constructor 2414
- BREAKING CHANGE: Fix the behavior of Doc.objects.limit(0) which should return all documents (similar to mongodb) 2311
- Bug fix in ListField when updating the first item, it was saving the whole list, instead of
just replacing the first item (as usually done when updating 1 item of the list) 2392
- Add EnumField: ``mongoengine.fields.EnumField``
- Refactoring - Remove useless code related to Document.__only_fields and Queryset.only_fields
- Fix query transformation regarding special operators 2365
- Bug Fix: Document.save() fails when shard_key is not _id 2154

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- ATTENTION: Drop support for Python2
- Add Mongo 4.0 to Travis
- Fix error when setting a string as a ComplexDateTimeField 2253
- Bump development Status classifier to Production/Stable 2232
- Improve Queryset.get to avoid confusing MultipleObjectsReturned message in case multiple match are found 630
- Fixed a bug causing inaccurate query results, while combining ``__raw__`` and regular filters for the same field 2264
- Add support for the `elemMatch` projection operator in .fields() (e.g BlogPost.objects.fields(elemMatch__comments="test")) 2267
- DictField validate failed without default connection (bug introduced in 0.19.0) 2239
- Remove methods that were deprecated years ago:
- name parameter in Field constructor e.g `StringField(name="...")`, was replaced by db_field
- Queryset.slave_okay() was deprecated since pymongo3
- dropDups was dropped with MongoDB3
- ``Queryset._ensure_indexes`` and ``Queryset.ensure_indexes``, the right method to use is ``Document.ensure_indexes``
- Added pre-commit for development/CI 2212
- Renamed requirements-lint.txt to requirements-dev.txt 2212
- Support for setting ReadConcern 2255

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- Tests require 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

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- 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.