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 from django.utils.encoding import python_2_unicode_compatible 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), ) @python_2_unicode_compatible 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 self._hints = {} def __str__(self): """ Return "app_label.model_label.manager_name". """ model = self.model opts = model._meta app = model._meta.app_label manager_name = next(name for (_, name, manager) in opts.concrete_managers + opts.abstract_managers if manager == self) return '%s.%s.%s' % (app, model._meta.object_name, manager_name) def check(self, **kwargs): return [] @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=None, hints=None): obj = copy.copy(self) obj._db = using or self._db obj._hints = hints or self._hints return obj @property def db(self): return self._db or router.db_for_read(self.model, **self._hints) ####################### # PROXIES TO QUERYSET # ####################### 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, hints=self._hints) 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()