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288 lines
7.7 KiB
ReStructuredText
288 lines
7.7 KiB
ReStructuredText
====================
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Django's Model._meta
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====================
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Currently django implements most of its behaviour that makes using models so
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nice using a metaclass. A metaclass is invoked when an actual class is created
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and can change that class' behaviour by adding or modifing its attributes and
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methods. This means that django is actually changing your model class at the
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moment when the ``models.py`` file of your app is loaded.
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One of those changes is that the model's metaclass takes the specified
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``Meta`` options that the model has attached to and uses it's attributes in
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conjunction with the model's fields to create a new attribute on the model
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that is called ``_meta``. This is then responsible for providing an API to
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access all database related information like the name of the database table or
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a list of all available fields.
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Django doesn't currently have an official documentation of the ``_meta``'s
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semantics, however it is kind of a stable API since many projects and all the
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db related django internals depend on it. And this page is about documenting
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the semantics of ``_meta``.
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Trivia
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======
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The ``Model._meta`` attribute is an instance of the
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``django.db.models.options.Options`` class. It gets attached to the model at
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that time when the model class is created by the
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``django.db.models.base.ModelBase`` metaclass.
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If ``_meta`` is mentioned we speak about the autogenerated ``_meta``
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attribute that is attached to the model class.
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Some clarifying: In the following text ``Meta`` is referring to the actual
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``class Meta:`` definition that the app author has put inside the model class.
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Like here::
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class Restaurant(models.Model):
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# ... some fields here ...
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class Meta:
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ordering = ('name',)
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Attributes copied from ``Meta``
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===============================
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.. the django intersphinx link doesn't work :-(
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Some of ``_meta``'s attributes are just copied from the ``Meta`` options. The
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following attributes are those. Their behaviour is more detailed described in
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the :doc:`django documentation <django:/ref/models/options>`.
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``abstract``
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A boolean value.
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See the django documentation on :attr:`~django.db.models.Options.abstract`
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for more information.
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``app_label``
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By default it is the name of the app module that the model was created in.
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This can be overriden in ``Meta`` to make a model part of a specific
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app.
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Also see the django documentation about
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:attr:`~django.db.models.Options.app_label`.
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``db_table``
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Contains the name of the database table used for this model. This is
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either what was set on ``Meta`` or defaults to a string that is built
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from ``app_label`` and ``model_name`` seperated by an underscore. So for
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example the ``db_table`` for ``django.contrib.auth.models.User`` is
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``'auth_user'``.
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Also see the django documentation about
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:attr:`~django.db.models.Options.db_table`.
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``db_tablespace``
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See the django documentation on
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:attr:`~django.db.models.Options.db_tablespace` for more information.
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``get_latest_by``
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The name of the field that should be used during ordering to make
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:meth:`~django.db.models.query.QuerySet.latest` and
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:meth:`~django.db.models.query.QuerySet.earliest` work.
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Also see the django documentation about
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:attr:`~django.db.models.Options.get_latest_by`.
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``managed``
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If ``managed`` is ``True`` then the :djadmin:`syncdb` management command will take care of creating the database tables. Defaults to ``True``.
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Also see the django documentation about
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:attr:`~django.db.models.Options.managed`.
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``order_with_respect_to``
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See the django documentation on
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:attr:`~django.db.models.Options.order_with_respect_to` for more information.
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``ordering``
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See the django documentation on
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:attr:`~django.db.models.Options.ordering` for more information.
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``permissions``
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See the django documentation on
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:attr:`~django.db.models.Options.permissions` for more information.
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``proxy``
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If set to ``True`` then this model will be treated a :ref:`proxy model
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<proxy-models>`.
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Also see the django documentation about
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:attr:`~django.db.models.Options.proxy`.
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``index_together``
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See the django documentation on
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:attr:`~django.db.models.Options.index_together` for more information.
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``unique_together``
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See the django documentation on
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:attr:`~django.db.models.Options.unique_together` for more information.
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``verbose_name``
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A human-readable name of the models name, singular. If this is not set in
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``Meta``, django will try to guess a human readable name by using the
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``object_name`` and inserting appropriate spaces for the CamelCased model
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name and then making everything lowercase.
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See the django documentation on
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:attr:`~django.db.models.Options.verbose_name` for more information.
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``verbose_name_plural``
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A human-readable name of the models name, plural. If this is not set in
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``Meta``, it will default to ``verbose_name`` + ``"s"``.
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See the django documentation on
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:attr:`~django.db.models.Options.verbose_name_plural` for more information.
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Attributes
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==========
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``abstract_managers``
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To handle various inheritance situations, we need to track where
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managers came from (concrete or abstract base classes).
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..
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``admin``
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Is ``None``. Doesn't seem to be used anywhere. So we don't need to
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document it.
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TODO: Create a django ticket to suggest removing it.
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``auto_created``
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TODO ...
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``auto_field``
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TODO ...
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``concrete_managers``
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TODO ...
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``concrete_model``
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TODO ...
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``has_auto_field``
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TODO ...
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``local_fields``
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TODO ...
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``local_many_to_many``
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TODO ...
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``model``
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This is the actual ``django.db.models.Model`` that the ``_meta`` attribute
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is attached to.
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``model_name``
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TODO ...
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``object_name``
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It is the actual name of the model class.
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``parents``
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TODO ...
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``pk``
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TODO ...
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``proxy_for_model``
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For any class that is a proxy (including automatically created
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classes for deferred object loading), ``proxy_for_model`` tells us
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which class this model is proxying. Note that ``proxy_for_model``
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can create a chain of proxy models. For non-proxy models, the
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variable is always ``None``.
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``related_fkey_lookups``
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List of all lookups defined in ForeignKey 'limit_choices_to' options
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from *other* models. Needed for some admin checks. Internal use only.
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``swappable``
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TODO ...
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``virtual_fields``
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TODO ...
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Methods
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=======
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``module_name(self)``
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TODO ...
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``add_field(self, field)``
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TODO ...
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``add_virtual_field(self, field)``
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TODO ...
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``setup_pk(self, field)``
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TODO ...
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``pk_index(self)``
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TODO ...
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``setup_proxy(self, target)``
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TODO ...
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``verbose_name_raw(self)``
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TODO ...
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``fields(self)``
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TODO ...
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``concrete_fields(self)``
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TODO ...
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``local_concrete_fields(self)``
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TODO ...
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``get_fields_with_model(self)``
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TODO ...
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``get_concrete_fields_with_model(self)``
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TODO ...
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``get_m2m_with_model(self)``
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TODO ...
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``get_field(self, name, many_to_many=True)``
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TODO ...
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``get_field_by_name(self, name)``
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TODO ...
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``get_all_field_names(self)``
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TODO ...
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``init_name_map(self)``
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TODO ...
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``get_add_permission(self)``
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TODO ...
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``get_change_permission(self)``
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TODO ...
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``get_delete_permission(self)``
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TODO ...
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``get_all_related_objects(self, local_only=False, include_hidden=False``
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TODO ...
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``get_all_related_objects_with_model(self, local_only=False``
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TODO ...
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``get_all_related_many_to_many_objects(self, local_only=False)``
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TODO ...
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``get_all_related_m2m_objects_with_model(self)``
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TODO ...
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``get_base_chain(self, model)``
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TODO ...
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``get_parent_list(self)``
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TODO ...
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``get_ancestor_link(self, ancestor)``
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TODO ...
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