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Custom Managers, Querysets & Manager Inheritance
================================================
Using a Custom Manager
----------------------
A nice feature of Django is the possibility to define one's own custom object managers.
This is fully supported with django_polymorphic: For creating a custom polymorphic
manager class, just derive your manager from ``PolymorphicManager`` instead of
``models.Manager``. As with vanilla Django, in your model class, you should
explicitly add the default manager first, and then your custom manager::
from polymorphic import PolymorphicModel, PolymorphicManager
class TimeOrderedManager(PolymorphicManager):
def get_queryset(self):
qs = super(TimeOrderedManager,self).get_queryset()
return qs.order_by('-start_date') # order the queryset
def most_recent(self):
qs = self.get_queryset() # get my ordered queryset
return qs[:10] # limit => get ten most recent entries
class Project(PolymorphicModel):
objects = PolymorphicManager() # add the default polymorphic manager first
objects_ordered = TimeOrderedManager() # then add your own manager
start_date = DateTimeField() # project start is this date/time
The first manager defined ('objects' in the example) is used by
Django as automatic manager for several purposes, including accessing
related objects. It must not filter objects and it's safest to use
the plain ``PolymorphicManager`` here.
Note that get_query_set is deprecated in Django 1.8 and creates warnings in Django 1.7.
Manager Inheritance
-------------------
Polymorphic models inherit/propagate all managers from their
base models, as long as these are polymorphic. This means that all
managers defined in polymorphic base models continue to work as
expected in models inheriting from this base model::
from polymorphic import PolymorphicModel, PolymorphicManager
class TimeOrderedManager(PolymorphicManager):
def get_queryset(self):
qs = super(TimeOrderedManager,self).get_queryset()
return qs.order_by('-start_date') # order the queryset
def most_recent(self):
qs = self.get_queryset() # get my ordered queryset
return qs[:10] # limit => get ten most recent entries
class Project(PolymorphicModel):
objects = PolymorphicManager() # add the default polymorphic manager first
objects_ordered = TimeOrderedManager() # then add your own manager
start_date = DateTimeField() # project start is this date/time
class ArtProject(Project): # inherit from Project, inheriting its fields and managers
artist = models.CharField(max_length=30)
ArtProject inherited the managers ``objects`` and ``objects_ordered`` from Project.
``ArtProject.objects_ordered.all()`` will return all art projects ordered
regarding their start time and ``ArtProject.objects_ordered.most_recent()``
will return the ten most recent art projects.
.
Note that get_query_set is deprecated in Django 1.8 and creates warnings in Django 1.7.
Using a Custom Queryset Class
-----------------------------
The ``PolymorphicManager`` class accepts one initialization argument,
which is the queryset class the manager should use. Just as with vanilla Django,
you may define your own custom queryset classes. Just use PolymorphicQuerySet
instead of Django's QuerySet as the base class::
from polymorphic import PolymorphicModel, PolymorphicManager, PolymorphicQuerySet
class MyQuerySet(PolymorphicQuerySet):
def my_queryset_method(...):
...
class MyModel(PolymorphicModel):
my_objects=PolymorphicManager(MyQuerySet)
...
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