django_prefetch_utils.selector

This module provides utilities for changing the implementation of prefetch_related_objects that Django uses. In order for these to work, enable_fetch_related_objects_selector() must be called. This will be done in AppConfig.ready if django_prefetch_utils is added to INSTALLED_APPS.

Once that has been called, then set_default_prefetch_related_objects() can be called to override the default implementation globally:

from django_prefetch_related.selector import set_default_prefetch_related_objects
from django_prefetch_utils.identity_map import prefetch_related_objects

set_default_prefetch_related_objects(prefetch_related_objects)

This will be done as part of AppConfig.ready if the PREFETCH_UTILS_DEFAULT_IMPLEMENTATION setting is provided.

To change the implementation used on a local basis, the override_prefetch_related_objects() or use_original_prefetch_related_objects() context decorators can be used:

from django_prefetch_utils.identity_map import prefetch_related_objects

@use_original_prefetch_related_objects()
def some_function():
    dogs = list(Dog.objects.all())  # uses Django's implementation

    with override_prefetch_related_objects(prefetch_related_objects):
        toys = list(Toy.objects.all)  # uses identity map implementation

disable_prefetch_related_objects_selector()

Changes django.db.models.query.prefetch_related_objects to Django’s original implementation of prefetch_related_objects.

enable_prefetch_related_objects_selector()

Changes django.db.models.query.prefetch_related_objects to an implemention which allows thread-local overrides.

get_prefetch_related_objects()

Returns the active implementation of prefetch_related_objects:

>>> from django_prefetch_utils.selector import get_prefetch_related_objects
>>> get_prefetch_related_objects()
<function django.db.models.query.prefetch_related_objects>

Returns:a function

class override_prefetch_related_objects(func)

This context decorator allows one to chnage the implementation of prefetch_related_objects to be func.

When the context manager or decorator exits, the implementation will be restored to its previous value.

with override_prefetch_related_objects(prefetch_related_objects):
    dogs = list(Dog.objects.prefetch_related('toys'))

Note

This requires enable_prefetch_related_objects_selector() to be run before the changes are able to take effect.

remove_default_prefetch_related_objects()

Removes a custom default implementation of prefetch_related_objects:

>>> set_default_prefetch_related_objects(some_implementation)
>>> get_prefetch_related_objects()
<function some_implementation>
>>> remove_default_prefetch_related_objects()
>>> get_prefetch_related_objects()
<function django.db.models.query.prefetch_related_objects>

set_default_prefetch_related_objects(func)

Sets the default implementation of prefetch_related_objects to be func:

>>> get_prefetch_related_objects()
<function django.db.models.query.prefetch_related_objects>
>>> set_default_prefetch_related_objects(some_implementation)
>>> get_prefetch_related_objects()
<function some_implementation>

class use_original_prefetch_related_objects

This context decorator allows one to force the prefetch_related_objects implementation to be Django’s default implementation:

with use_original_prefetch_related_objects():
    dogs = list(Dog.objects.prefetch_related('toys'))