charettes / django-delegate

Automatic delegate methods for Django managers and querysets without runtime dispatch penalties.

django-delegate

With django-delegate, you get AUTOMATICALLY CHAINABLE MANAGER/QUERYSET DELEGATE METHODS.

Normally, by defining manager methods, Django lets you do this:

>>> SomeModel.objects.custom_query()

... but it WON'T let you do this:

>>> SomeModel.objects.custom_query().another_custom_query()

... unless you duplicate your methods and define a redundant queryset subclass... UNTIL NOW.

With DelegateManager and @delegate, you can write maintainable custom-query logic with free chaining. instead of defining manager methods, you define queryset methods, decorate those you'd like to delegate, and a two-line DelegateManager subclass specifying the queryset. ET VIOLA. Like so:

from delegate import DelegateManager, delegate

class CustomQuerySet(models.query.QuerySet):

    @delegate
    def qs_method(self, some_value):
        return self.filter(some_param__icontains=some_value)

    def dont_delegate_me(self):
        return self.filter(some_other_param="something else")

class CustomManager(DelegateManager):
    __queryset__ = CustomQuerySet

class SomeModel(models.Model):
    objects = CustomManager()


# this will work:
SomeModel.objects.qs_method('yo dogg')
# this will also work:
SomeModel.objects.qs_method('yo dogg').qs_method('i heard you like queryset method delegation')

To delegate all of the methods in a QuerySet automatically, you can create a subclass of DelegateQuerySet. These two QuerySet subclasses work identically:

from delegate import DelegateQuerySet, delegate

class ManualDelegator(models.query.QuerySet):
    @delegate
    def qs_method(self):
        # ...

class AutomaticDelegator(DelegateQuerySet):
    def qs_method(self):
        # ...

You can also apply the @delegate decorator directly to a class -- this permits you to delegate all the methods in a class without disrupting its inheritance chain. This example works identically to the previous two:

from delegate import delegate

@delegate
class CustomQuerySet(models.query.QuerySet):

    def qs_method(self, some_value):
        return self.filter(some_param__icontains=some_value)