Extended the release notes for chainable Manager/QuerySet methods.
Refs #20625.
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@ -127,9 +127,40 @@ to call the method on the superclass and simply add or remove extra arguments.
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Calling custom ``QuerySet`` methods from the ``Manager``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Historically, the recommended way to make reusable model queries was to create
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methods on a custom ``Manager`` class. The problem with this approach was that
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after the first method call, you'd get back a ``QuerySet`` instance and
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couldn't call additional custom manager methods.
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Though not documented, it was common to work around this issue by creating a
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custom ``QuerySet`` so that custom methods could be chained; but the solution
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had a number of drawbacks:
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* The custom ``QuerySet`` and its custom methods were lost after the first
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call to ``values()`` or ``values_list()``.
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* Writing a custom ``Manager`` was still necessary to return the custom
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``QuerySet`` class and all methods that were desired on the ``Manager``
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had to be proxied to the ``QuerySet``. The whole process went against
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the DRY principle.
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The :meth:`QuerySet.as_manager() <django.db.models.query.QuerySet.as_manager>`
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class method has been added to :ref:`create Manager with QuerySet methods
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<create-manager-with-queryset-methods>`.
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class method can now directly :ref:`create Manager with QuerySet methods
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<create-manager-with-queryset-methods>`::
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class FoodQuerySet(models.QuerySet):
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def pizzas(self):
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return self.filter(kind='pizza')
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def vegetarian(self):
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return self.filter(vegetarian=True)
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class Food(models.Model):
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kind = models.CharField(max_length=50)
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vegetarian = models.BooleanField()
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objects = FoodQuerySet.as_manager()
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Food.objects.pizzas().vegetarian()
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Using a custom manager when traversing reverse relations
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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