import copy
import inspect
from importlib import import_module
from django.db import router
from django.db.models.query import QuerySet
class BaseManager:
# To retain order, track each time a Manager instance is created.
creation_counter = 0
# Set to True for the 'objects' managers that are automatically created.
auto_created = False
#: 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):
# Capture the arguments to make returning them trivial.
obj = super().__new__(cls)
obj._constructor_args = (args, kwargs)
return obj
def __init__(self):
super().__init__()
self._set_creation_counter()
self.model = None
self.name = None
self._db = None
self._hints = {}
def __str__(self):
"""Return "app_label.model_label.manager_name"."""
return '%s.%s' % (self.model._meta.label, self.name)
def deconstruct(self):
"""
Return a 5-tuple of the form (as_manager (True), manager_class,
queryset_class, args, kwargs).
Raise 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 = {}
for name, method in inspect.getmembers(queryset_class, predicate=inspect.isfunction):
# 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__)
return type(class_name, (cls,), {
'_queryset_class': queryset_class,
**cls._get_queryset_methods(queryset_class),
})
def contribute_to_class(self, model, name):
self.name = self.name or name
self.model = model
setattr(model, name, ManagerDescriptor(self))
model._meta.add_manager(self)
def _set_creation_counter(self):
"""
Set the creation counter value for this instance and increment the
class-level copy.
"""
self.creation_counter = BaseManager.creation_counter
BaseManager.creation_counter += 1
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):
"""
Return a new QuerySet object. Subclasses can override this method to
customize the behavior of the Manager.
"""
return self._queryset_class(model=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 __hash__(self):
return id(self)
class Manager(BaseManager.from_queryset(QuerySet)):
pass
class ManagerDescriptor:
def __init__(self, manager):
self.manager = manager
def __get__(self, instance, cls=None):
if instance is not None:
raise AttributeError("Manager isn't accessible via %s instances" % cls.__name__)
if cls._meta.abstract:
raise AttributeError("Manager isn't available; %s is abstract" % (
cls._meta.object_name,
))
if cls._meta.swapped:
raise AttributeError(
"Manager isn't available; '%s.%s' has been swapped for '%s'" % (
cls._meta.app_label,
cls._meta.object_name,
cls._meta.swapped,
)
)
return cls._meta.managers_map[self.manager.name]
class EmptyManager(Manager):
def __init__(self, model):
super().__init__()
self.model = model
def get_queryset(self):
return super().get_queryset().none()