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76 lines
2.6 KiB
Text
76 lines
2.6 KiB
Text
==================
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django-model-utils
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==================
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Django model mixins and utilities.
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models.InheritanceCastModel
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===========================
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This abstract base class can be inherited by the root (parent) model
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in a model-inheritance tree. It allows each model in the tree to
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"know" what type it is (via an automatically-set foreign key to
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``ContentType``), allowing for automatic casting of a parent instance
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to its proper leaf (child) type.
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For instance, if you have a ``Place`` model with subclasses
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``Restaurant`` and ``Bar``, you may want to query all Places::
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nearby_places = Place.objects.filter(location='here')
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But when you iterate over ``nearby_places``, you'll get only ``Place``
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instances back, even for objects that are "really" ``Restaurant`` or
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``Bar``. If you have ``Place`` inherit from ``InheritanceCastModel``,
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you can just call the ``cast()`` method on each ``Place`` and it will
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return an instance of the proper subtype, ``Restaurant`` or ``Bar``::
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from model_utils.models import InheritanceCastModel
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class Place(InheritanceCastModel):
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...
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class Restaurant(Place):
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...
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nearby_places = Place.objects.filter(location='here')
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for place in nearby_places:
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restaurant_or_bar = place.cast()
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...
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.. note::
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This is inefficient for large querysets, as it results in n
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queries to the subtype tables. It would be possible to write a
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QuerySet subclass that could reduce this to k queries, where there
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are k subtypes in the inheritance tree.
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models.TimeStampedModel
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=======================
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This abstract base class just provides self-updating ``created`` and
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``modified`` fields on any model that inherits it.
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managers.QueryManager
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=====================
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Many custom model managers do nothing more than return a QuerySet that
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is filtered in some way. ``QueryManager`` allows you to express this
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pattern with a minimum of boilerplate::
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from django.db import models
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from model_utils.managers import QueryManager
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class Post(models.Model):
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...
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published = models.BooleanField()
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pub_date = models.DateField()
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...
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objects = models.Manager()
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public = QueryManager(published=True).order_by('-pub_date')
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The kwargs passed to ``QueryManager`` will be passed as-is to the
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``QuerySet.filter()`` method. You can also pass a ``Q`` object to
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``QueryManager`` to express more complex conditions. Note that you can
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set the ordering of the ``QuerySet`` returned by the ``QueryManager``
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by chaining a call to ``.order_by()`` on the ``QueryManager`` (this is
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not required).
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