Known issues and limitations

This document summarizes some known issues and limitations of this library. If you notice an issue not listed, use the Issue tracker to report a bug or request a feature.

Like any database, MongoDB has some particularities. Also keep in mind that because MongoDB is a NoSQL database, it’s impossible to implement SQL-specific functionality.

Model fields

• DateTimeField is limited to millisecond precision (rather than microsecond like most other databases), and correspondingly, DurationField stores milliseconds rather than microseconds.

• Some of Django’s built-in fields aren’t supported by MongoDB:

  • AutoField (including BigAutoField and SmallAutoField)

  • CompositePrimaryKey

  • GeneratedField

Querying

• The following QuerySet methods aren’t supported:

  • difference()

  • extra()

  • intersection()

  • prefetch_related()

  • raw() (use raw_aggregate() instead)

  • select_for_update() (acts as a no-op)

• QuerySet.delete() and update() do not support queries that span multiple collections.

• The StringAgg aggregation function isn’t supported.

• When querying JSONField:

  • There is no way to distinguish between a JSON "null" (represented by Value(None, JSONField())) and a SQL null (queried using the isnull lookup). Both of these queries return both of these nulls.

  • Some queries with Q objects, e.g. Q(value__foo="bar"), don’t work properly, particularly with QuerySet.exclude().

  • Filtering for a None key, e.g. QuerySet.filter(value__j=None) incorrectly returns objects where the key doesn’t exist.

  • You can study the skipped tests in DatabaseFeatures.django_test_skips for more details on known issues.

• Pattern matching lookups (iexact, startswith, istartswith, endswith, iendswith, contains, icontains, regex, and iregex) don’t support non-string fields.

Database functions

• Some of Django’s built-in database functions aren’t supported by MongoDB:

  • Chr

  • ExtractQuarter

  • LPad, RPad

  • MD5

  • Now

  • Ord

  • Repeat

  • Reverse

  • Right

  • SHA1, SHA224, SHA256, SHA384, SHA512

  • Sign

• The tzinfo parameter of the TruncDate and TruncTime database functions isn’t supported.

Transaction management

By default, query execution uses Django and MongoDB’s default behavior of autocommit mode. Each query is immediately committed to the database.

Django’s transaction management APIs are not supported. Instead, this package provides its own transaction APIs.

Database introspection

Due to the lack of ability to introspect MongoDB collection schema, inspectdb and migrate --fake-initial aren’t supported.

Caching

Database caching is not supported since Django’s built-in database cache backend requires SQL. A custom cache backend for MongoDB may be provided in the future.