234 lines
8.5 KiB
Python
234 lines
8.5 KiB
Python
import copy
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import inspect
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from django.db import router
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from django.db.models.query import QuerySet
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from django.db.models.fields import FieldDoesNotExist
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from django.utils import six
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from django.utils.encoding import python_2_unicode_compatible
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def ensure_default_manager(cls):
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"""
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Ensures that a Model subclass contains a default manager and sets the
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_default_manager attribute on the class. Also sets up the _base_manager
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points to a plain Manager instance (which could be the same as
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_default_manager if it's not a subclass of Manager).
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"""
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if cls._meta.abstract:
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setattr(cls, 'objects', AbstractManagerDescriptor(cls))
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return
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elif cls._meta.swapped:
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setattr(cls, 'objects', SwappedManagerDescriptor(cls))
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return
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if not getattr(cls, '_default_manager', None):
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# Create the default manager, if needed.
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try:
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cls._meta.get_field('objects')
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raise ValueError(
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"Model %s must specify a custom Manager, because it has a "
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"field named 'objects'" % cls.__name__
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)
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except FieldDoesNotExist:
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pass
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cls.add_to_class('objects', Manager())
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cls._base_manager = cls.objects
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elif not getattr(cls, '_base_manager', None):
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default_mgr = cls._default_manager.__class__
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if (default_mgr is Manager or
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getattr(default_mgr, "use_for_related_fields", False)):
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cls._base_manager = cls._default_manager
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else:
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# Default manager isn't a plain Manager class, or a suitable
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# replacement, so we walk up the base class hierarchy until we hit
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# something appropriate.
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for base_class in default_mgr.mro()[1:]:
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if (base_class is Manager or
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getattr(base_class, "use_for_related_fields", False)):
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cls.add_to_class('_base_manager', base_class())
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return
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raise AssertionError(
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"Should never get here. Please report a bug, including your "
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"model and model manager setup."
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)
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@python_2_unicode_compatible
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class BaseManager(object):
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# Tracks each time a Manager instance is created. Used to retain order.
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creation_counter = 0
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def __init__(self):
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super(BaseManager, self).__init__()
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self._set_creation_counter()
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self.model = None
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self.name = None
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self._inherited = False
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self._db = None
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self._hints = {}
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def __str__(self):
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""" Return "app_label.model_label.manager_name". """
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model = self.model
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app = model._meta.app_label
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return '%s.%s.%s' % (app, model._meta.object_name, self.name)
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def check(self, **kwargs):
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return []
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@classmethod
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def _get_queryset_methods(cls, queryset_class):
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def create_method(name, method):
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def manager_method(self, *args, **kwargs):
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return getattr(self.get_queryset(), name)(*args, **kwargs)
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manager_method.__name__ = method.__name__
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manager_method.__doc__ = method.__doc__
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return manager_method
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new_methods = {}
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# Refs http://bugs.python.org/issue1785.
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predicate = inspect.isfunction if six.PY3 else inspect.ismethod
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for name, method in inspect.getmembers(queryset_class, predicate=predicate):
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# Only copy missing methods.
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if hasattr(cls, name):
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continue
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# Only copy public methods or methods with the attribute `queryset_only=False`.
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queryset_only = getattr(method, 'queryset_only', None)
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if queryset_only or (queryset_only is None and name.startswith('_')):
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continue
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# Copy the method onto the manager.
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new_methods[name] = create_method(name, method)
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return new_methods
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@classmethod
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def from_queryset(cls, queryset_class, class_name=None):
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if class_name is None:
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class_name = '%sFrom%s' % (cls.__name__, queryset_class.__name__)
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class_dict = {
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'_queryset_class': queryset_class,
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}
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class_dict.update(cls._get_queryset_methods(queryset_class))
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return type(class_name, (cls,), class_dict)
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def contribute_to_class(self, model, name):
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# TODO: Use weakref because of possible memory leak / circular reference.
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self.model = model
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if not self.name:
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self.name = name
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# Only contribute the manager if the model is concrete
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if model._meta.abstract:
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setattr(model, name, AbstractManagerDescriptor(model))
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elif model._meta.swapped:
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setattr(model, name, SwappedManagerDescriptor(model))
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else:
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# if not model._meta.abstract and not model._meta.swapped:
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setattr(model, name, ManagerDescriptor(self))
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if (not getattr(model, '_default_manager', None) or
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self.creation_counter < model._default_manager.creation_counter):
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model._default_manager = self
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abstract = False
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if model._meta.abstract or (self._inherited and not self.model._meta.proxy):
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abstract = True
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model._meta.managers.append((self.creation_counter, self, abstract))
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def _set_creation_counter(self):
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"""
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Sets the creation counter value for this instance and increments the
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class-level copy.
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"""
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self.creation_counter = BaseManager.creation_counter
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BaseManager.creation_counter += 1
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def _copy_to_model(self, model):
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"""
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Makes a copy of the manager and assigns it to 'model', which should be
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a child of the existing model (used when inheriting a manager from an
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abstract base class).
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"""
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assert issubclass(model, self.model)
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mgr = copy.copy(self)
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mgr._set_creation_counter()
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mgr.model = model
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mgr._inherited = True
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return mgr
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def db_manager(self, using=None, hints=None):
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obj = copy.copy(self)
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obj._db = using or self._db
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obj._hints = hints or self._hints
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return obj
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@property
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def db(self):
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return self._db or router.db_for_read(self.model, **self._hints)
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#######################
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# PROXIES TO QUERYSET #
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#######################
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def get_queryset(self):
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"""
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Returns a new QuerySet object. Subclasses can override this method to
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easily customize the behavior of the Manager.
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"""
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return self._queryset_class(self.model, using=self._db, hints=self._hints)
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def all(self):
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# We can't proxy this method through the `QuerySet` like we do for the
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# rest of the `QuerySet` methods. This is because `QuerySet.all()`
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# works by creating a "copy" of the current queryset and in making said
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# copy, all the cached `prefetch_related` lookups are lost. See the
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# implementation of `RelatedManager.get_queryset()` for a better
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# understanding of how this comes into play.
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return self.get_queryset()
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class Manager(BaseManager.from_queryset(QuerySet)):
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pass
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class ManagerDescriptor(object):
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# This class ensures managers aren't accessible via model instances.
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# For example, Poll.objects works, but poll_obj.objects raises AttributeError.
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def __init__(self, manager):
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self.manager = manager
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def __get__(self, instance, type=None):
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if instance is not None:
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raise AttributeError("Manager isn't accessible via %s instances" % type.__name__)
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return self.manager
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class AbstractManagerDescriptor(object):
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# This class provides a better error message when you try to access a
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# manager on an abstract model.
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def __init__(self, model):
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self.model = model
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def __get__(self, instance, type=None):
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raise AttributeError("Manager isn't available; %s is abstract" % (
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self.model._meta.object_name,
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))
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class SwappedManagerDescriptor(object):
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# This class provides a better error message when you try to access a
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# manager on a swapped model.
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def __init__(self, model):
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self.model = model
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def __get__(self, instance, type=None):
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raise AttributeError("Manager isn't available; %s has been swapped for '%s'" % (
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self.model._meta.object_name, self.model._meta.swapped
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))
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class EmptyManager(Manager):
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def __init__(self, model):
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super(EmptyManager, self).__init__()
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self.model = model
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def get_queryset(self):
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return super(EmptyManager, self).get_queryset().none()
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