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from django.db.models.query import QuerySet
from django.dispatch import dispatcher
from django.db.models import signals
from django.db.models.fields import FieldDoesNotExist
# Size of each "chunk" for get_iterator calls.
# Larger values are slightly faster at the expense of more storage space.
GET_ITERATOR_CHUNK_SIZE = 100
def ensure_default_manager(sender):
cls = sender
if not hasattr(cls, '_default_manager'):
# 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())
dispatcher.connect(ensure_default_manager, signal=signals.class_prepared)
class Manager(object):
# Tracks each time a Manager instance is created. Used to retain order.
creation_counter = 0
def __init__(self):
super(Manager, self).__init__()
# Increase the creation counter, and save our local copy.
self.creation_counter = Manager.creation_counter
Manager.creation_counter += 1
self.model = None
def contribute_to_class(self, model, name):
# TODO: Use weakref because of possible memory leak / circular reference.
self.model = model
setattr(model, name, ManagerDescriptor(self))
if not hasattr(model, '_default_manager') or self.creation_counter < model._default_manager.creation_counter:
model._default_manager = self
#######################
# PROXIES TO QUERYSET #
#######################
def get_query_set(self):
"""Returns a new QuerySet object. Subclasses can override this method
to easily customise the behaviour of the Manager.
"""
return QuerySet(self.model)
def all(self):
return self.get_query_set()
def count(self):
return self.get_query_set().count()
def dates(self, *args, **kwargs):
return self.get_query_set().dates(*args, **kwargs)
def distinct(self, *args, **kwargs):
return self.get_query_set().distinct(*args, **kwargs)
def extra(self, *args, **kwargs):
return self.get_query_set().extra(*args, **kwargs)
def get(self, *args, **kwargs):
return self.get_query_set().get(*args, **kwargs)
def get_or_create(self, **kwargs):
return self.get_query_set().get_or_create(**kwargs)
def create(self, **kwargs):
return self.get_query_set().create(**kwargs)
def filter(self, *args, **kwargs):
return self.get_query_set().filter(*args, **kwargs)
def complex_filter(self, *args, **kwargs):
return self.get_query_set().complex_filter(*args, **kwargs)
def exclude(self, *args, **kwargs):
return self.get_query_set().exclude(*args, **kwargs)
def in_bulk(self, *args, **kwargs):
return self.get_query_set().in_bulk(*args, **kwargs)
def iterator(self, *args, **kwargs):
return self.get_query_set().iterator(*args, **kwargs)
def latest(self, *args, **kwargs):
return self.get_query_set().latest(*args, **kwargs)
def order_by(self, *args, **kwargs):
return self.get_query_set().order_by(*args, **kwargs)
def select_related(self, *args, **kwargs):
return self.get_query_set().select_related(*args, **kwargs)
def values(self, *args, **kwargs):
return self.get_query_set().values(*args, **kwargs)
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 != None:
raise AttributeError, "Manager isn't accessible via %s instances" % type.__name__
return self.manager
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