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DOCSP-46329 Add Limitations page (#12)
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‎source/index.txt

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Connection Configuration </connect>
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Model Your Data </model-data>
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Interact with Data </interact-data>
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Limitations </limitations>
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Issues & Help </issues-and-help>
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Compatibility </compatibility>
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API Documentation <{+api+}>
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.. TODO:
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Django Feature Limitations </feature-limitations>
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.. warning:: Public Preview
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Learn how to use {+django-odm+} to perform operations on MongoDB data
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in the :ref:`django-interact-data` section.
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.. TODO:
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.. Django Feature Limitations
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.. --------------------------
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Django Feature Limitations
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--------------------------
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.. Learn about the Django features that {+django-odm+} does not support
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in the :ref:`django-feature-limitations` section.
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Learn about the Django features that {+django-odm+} does not support
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in the :ref:`django-limitations` section.
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Compatibility
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-------------

‎source/limitations.txt

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.. _django-limitations:
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============
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Limitations
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============
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.. contents:: On this page
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:local:
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:backlinks: none
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:depth: 1
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:class: singlecol
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.. facet::
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:name: genre
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:values: reference
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.. meta::
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:keywords: support, features, django
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Overview
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--------
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On this page, you can find a list of features that
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{+django-odm+} does not support. Because {+django-odm+} is in active
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development, some features listed on this page might be considered for future
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releases based on user demand. You can request support for a feature by leaving
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a suggestion on the `Drivers Feedback Forum
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<https://feedback.mongodb.com/forums/924286-drivers?category_id=370732>`__.
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Unsupported Database Variables
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------------------------------
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The following database variables are not supported by {+django-odm+}:
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- ``ATOMIC_REQUESTS``
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- ``AUTOCOMMIT``
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- ``CONN_HEALTH_CHECKS``
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- ``TIME_ZONE``
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Model Limitations
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-----------------
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The following limitations apply to models in {+django-odm+}:
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- {+django-odm+} enforces a one-to-one mapping between a Django model and a
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MongoDB collection. Because of this, multiple models cannot share the same collection.
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Indexes
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~~~~~~~
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{+django-odm+} does not support the following index functionalities:
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- Creating ``$vectorSearch`` and ``$search`` indexes through the Django
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Indexes API
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- Creating geospatial indexes through the Django Indexes API
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- Updating indexes in ``EmbeddedModelFields`` after model creation
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To learn how to run unsupported database operations by operating directly on
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your ``MongoClient`` instance, see :ref:`django-client-operations` in the
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Perform Raw Database Queries guide.
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Fields
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~~~~~~
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{+django-odm+} has the following limitations on the specified field types:
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- ``ArrayField``
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- {+django-odm+} does not support ``ArrayField`` polymorphism.
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- {+django-odm+} does not support nesting an ``EmbeddedModelField`` within an ``ArrayField``.
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- ``EmbeddedModelField``
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- ``EmbeddedModel`` schema changes do not register after creation.
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- Embedded documents cannot take Django foreign keys.
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- {+django-odm+} does not support arbitrary or untyped embedded model
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fields. You must derive all fields from a ``EmbeddedModel`` class.
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- ``JSONField``
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- {+django-odm+} cannot distinguish between a JSON and a SQL ``null`` value.
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Queries that use ``Value(None, JSONField())`` or the ``isnull`` lookup
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return both JSON and SQL ``null`` values.
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- Some queries with ``Q`` objects, such as ``Q(value__foo="bar")``, might
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not work as expected.
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- Filtering for ``None`` values incorrectly returns objects in which a field
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does not exist.
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- ``DateTimeField``
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- {+django-odm+} does not support microsecond granularity for
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``DateTimeField``.
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- ``DurationField``
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- ``DurationField`` stores milliseconds rather than microseconds.
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- ``ForeignKey``
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- When possible, you should use an ``EmbeddedModelField`` instead of a
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``ForeignKey`` field to avoid using ``$lookup`` operations. An
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``EmbeddedModelField`` emulates a MongoDB embedded document and performs
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better than a ``ForeignKey`` field. To learn more about how to reduce
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``$lookup`` operations, see the :atlas:`Reduce $lookup Operations
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</schema-suggestions/reduce-lookup-operations/>` guide in the Atlas
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documentation.
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- Performance of `CASCADE deletes <{+django-docs+}/ref/models/fields/#django.db.models.CASCADE>`__
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on a ``ForeignKey`` field is not as performant as using an
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``EmbeddedModelField``.
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The following field types are unavailable in {+django-odm+}:
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- ``GeneratedField``
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- ``AutoField``
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- ``BigAutoField``
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- ``SmallAutoField``
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Querying Limitations
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--------------------
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{+django-odm+} does not support the following ``QuerySet`` API methods:
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- ``distinct()``
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- ``dates()``
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- ``datetimes()``
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- ``prefetch_related()``
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- ``extra()``
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{+django-odm+} does not support ``QuerySet.delete()`` and ``update()`` queries
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that span multiple collections.
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Geospatial Queries
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~~~~~~~~~~~~~~~~~~
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- {+django-odm+} does not support ``GeoDjango``.
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- {+django-odm+} does not have any Django lookup operators for MongoDB-specific
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geospatial queries.
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Aggregation Operators
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~~~~~~~~~~~~~~~~~~~~~
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{+django-odm+} does not contain any custom Django field lookups for the MongoDB
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aggregation framework. Instead, use the ``raw_aggregate()`` method. For more
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information on the ``raw_aggregate()`` method, see
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the :ref:`django-raw-queries` guide.
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.. TODO: Link to aggregation
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Database Functions
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~~~~~~~~~~~~~~~~~~
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{+django-odm+} does not support the following database functions:
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- ``Chr``
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- ``ExtractQuarter``
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- ``MD5``
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- ``Now``
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- ``Ord``
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- ``Pad``
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- ``Repeat``
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- ``Reverse``
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- ``Right``
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- ``SHA1``, ``SHA224``, ``SHA256``, ``SHA384``, ``SHA512``
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- ``Sign``
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The ``tzinfo`` parameter of the ``Trunc`` database functions doesn't work
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properly because MongoDB converts the result back to UTC.
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Django Management Command Limitations
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-------------------------------------
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{+django-odm+} does not support the following Django management commands:
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- ``createcachetable``
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- ``inspectdb``
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- ``optimizemigration``
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- ``sqlflush``
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- ``sqlsequencereset``
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Migration Limitations
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---------------------
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- {+django-odm+} does not support enforced schema validation. To learn how to
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enforce schema validation in your application, see the :manual:`Specify JSON
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Schema Validation </core/schema-validation/specify-json-schema/>` guide in the
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{+mdb-server+} manual.
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- {+django-odm+} does not support `DDL Transactions
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<{+django-docs+}/topics/migrations/#transactions>`__.
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- {+django-odm+} does not support the ``migrate --fake-initial`` command.
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Asynchronous Support
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--------------------
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{+django-odm+} has not been tested for support of the asynchronous functionality of
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the Django API.
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Data Types
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----------
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{+django-odm+} does not have a custom ``Field`` class for the ``BSONRegExp``
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data type. Instead, use the ``CharField`` class.
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Performance
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-----------
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The engineering team is prioritizing feature development for the Public Preview
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release of {+django-odm+}. Because of this, you might notice performance
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limitations with certain workloads. If you encounter any performance issues,
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please report them as shown in the :ref:`Issues & Help <django-issues-and-help>`
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guide. You can also share your feedback on the `Drivers Feedback Forum
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<https://feedback.mongodb.com/forums/924286-drivers?category_id=370732>`__.

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