Source code for django.db.models.manager
import copy
import inspect
from importlib import import_module
from django.db import router
from django.db.models.query import QuerySet
from django.utils import six
from django.utils.encoding import python_2_unicode_compatible
def ensure_default_manager(cls):
"""
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).
"""
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):
if any(f.name == 'objects' for f in cls._meta.fields):
raise ValueError(
"Model %s must specify a custom Manager, because it has a "
"field named 'objects'" % cls.__name__
)
# Create the default manager, if needed.
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."
)
@python_2_unicode_compatible
class BaseManager(object):
# Tracks each time a Manager instance is created. Used to retain order.
creation_counter = 0
#: If set to True the manager will be serialized into migrations and will
#: thus be available in e.g. RunPython operations
use_in_migrations = False
def __new__(cls, *args, **kwargs):
# We capture the arguments to make returning them trivial
obj = super(BaseManager, cls).__new__(cls)
obj._constructor_args = (args, kwargs)
return obj
def __init__(self):
super(BaseManager, self).__init__()
self._set_creation_counter()
self.model = None
self.name = None
self._inherited = False
self._db = None
self._hints = {}
def __str__(self):
""" Return "app_label.model_label.manager_name". """
model = self.model
app = model._meta.app_label
return '%s.%s.%s' % (app, model._meta.object_name, self.name)
def deconstruct(self):
"""
Returns a 5-tuple of the form (as_manager (True), manager_class,
queryset_class, args, kwargs).
Raises a ValueError if the manager is dynamically generated.
"""
qs_class = self._queryset_class
if getattr(self, '_built_with_as_manager', False):
# using MyQuerySet.as_manager()
return (
True, # as_manager
None, # manager_class
'%s.%s' % (qs_class.__module__, qs_class.__name__), # qs_class
None, # args
None, # kwargs
)
else:
module_name = self.__module__
name = self.__class__.__name__
# Make sure it's actually there and not an inner class
module = import_module(module_name)
if not hasattr(module, name):
raise ValueError(
"Could not find manager %s in %s.\n"
"Please note that you need to inherit from managers you "
"dynamically generated with 'from_queryset()'."
% (name, module_name)
)
return (
False, # as_manager
'%s.%s' % (module_name, name), # manager_class
None, # qs_class
self._constructor_args[0], # args
self._constructor_args[1], # kwargs
)
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
if not self.name:
self.name = name
# 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
abstract = False
if model._meta.abstract or (self._inherited and not self.model._meta.proxy):
abstract = True
model._meta.managers.append((self.creation_counter, self, abstract))
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()
def __eq__(self, other):
return (
isinstance(other, self.__class__) and
self._constructor_args == other._constructor_args
)
def __ne__(self, other):
return not (self == other)
def __hash__(self):
return id(self)
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()
