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