Django GetOrCreatePlus
Django GetOrCreatePlus is a set of queryset mixins to create custom querysets that can:
- Cache results of get_or_create() or update_or_create()
- Always use get_or_create() when get() calls are made
- Allow non-atomic get_or_create() to avoid nested transaction points
Quick start
# models.py
from django.db import models
from django.core.cache import caches
from getorcreateplus import CachedGetOrCreateMixin, AlwaysGetOrCreateMixin, NonAtomicGetOrCreateMixin
# sample for CachedGetOrCreateMixin (see below for changes to be made in settings.py)
class CachedQuerySet(CachedGetOrCreateMixin, models.QuerySet):
pass
class CachedManager(models.manager.BaseManager.from_queryset(CachedQuerySet)):
use_for_related_fields = True
class CachedImmutableModel(models.Model):
foo = models.CharField(max_length=8)
bar = models.IntegerField(null=True)
objects = CachedManager()
obj1, _ = CachedImmutableModel.objects.get_or_create(foo='FooBar') # fetches from db
obj2, _ = CachedImmutableModel.objects.get_or_create(foo='FooBar') # hits cache
class CachedMutableObject(models.Model):
foo = models.CharField(max_length=8)
bar = models.IntegerField(null=True)
objects = CachedManager()
def save(self, **kwargs):
cache = caches[self._meta.model_name]
cache.delete(self.pk)
return super(CachedMutableObject, self).save(**kwargs)
obj1, _ = CachedMutableModel.objects.get_or_create(foo='FooBar') # fetches from db
obj1.bar = 1
obj1.save() # invalidate object cache
obj2, _ = CachedMutableModel.objects.get_or_create(foo='FooBar') # fetches from db
obj3, _ = CachedMutableModel.objects.get_or_create(foo='FooBar') # hits cache
# sample for NonAtomicGetOrCreateMixin
class NonAtomicQuerySet(NonAtomicGetOrCreateMixin, models.QuerySet):
pass
class NonAtomicManager(models.manager.BaseManager.from_queryset(NonAtomicQuerySet)):
use_for_related_fields = True
class ParentQuerySet(NonAtomicQuerySet):
def create(self, **kwargs):
children = kwargs.pop('children', [])
parent = super(ParentQuerySet, self).create(**kwargs)
for child in children:
parent.children.get_or_create(**child)
return parent
class ParentManager(models.manager.BaseManager.from_queryset(ParentQuerySet)):
use_for_related_fields = True
class ParentModel(models.Model):
foo = models.CharField(max_length=8)
objects = ParentManager()
class ChildModel(models.Model):
parent = models.ForeignKey(Parent, related_name='children')
bar = models.CharField(max_length=8)
objects = NonAtomicManager()
from django.db import transaction
with transaction.atomic():
parent, _ = ParentModel.objects.get_or_create(foo='Foo', defaults={children: [{bar: 'Bar'}, {bar: 'Baz'}]})
# samples for combining mixins CachedGetOrCreateMixin, AlwaysGetOrCreateMixin, NonAtomicGetOrCreateMixin
class NonAtomicAlwaysQuerySet(NonAtomicGetOrCreateMixin, AlwaysGetOrCreateMixin, models.QuerySet):
pass
class AlwaysCachedQuerySet(AlwaysGetOrCreateMixin, CachedGetOrCreateMixin, models.QuerySet):
pass
class PlusQuerySet(CachedGetOrCreateMixin, AlwaysGetOrCreateMixin, NonAtomicGetOrCreateMixin, models.QuerySet):
passCachedGetOrCreateMixin uses Django caches. The keys are cached to the default cache, and the objects are cached using alias model._meta.model_name.
NOTE: If you have models by the same name in different apps both using CachedGetOrCreateMixin, this will fail.
# settings.py
# assuming use of django-connection-url (shameless self-plug)
import connection_url
CACHES = {
'default': connection_url.config('locmem:///'),
'cachedimmutablemodel': connection_url.config('REDIS_URL'),
'cachedmutablemodel': connection_url.config('MEMCACHED_URL'),
}
