214 lines
6.7 KiB
Python
214 lines
6.7 KiB
Python
import copy
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import inspect
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from functools import wraps
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from importlib import import_module
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from django.db import router
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from django.db.models.query import QuerySet
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class BaseManager:
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# To retain order, track each time a Manager instance is created.
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creation_counter = 0
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# Set to True for the 'objects' managers that are automatically created.
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auto_created = False
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#: If set to True the manager will be serialized into migrations and will
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#: thus be available in e.g. RunPython operations.
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use_in_migrations = False
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def __new__(cls, *args, **kwargs):
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# Capture the arguments to make returning them trivial.
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obj = super().__new__(cls)
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obj._constructor_args = (args, kwargs)
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return obj
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def __init__(self):
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super().__init__()
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self._set_creation_counter()
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self.model = None
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self.name = None
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self._db = None
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self._hints = {}
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def __str__(self):
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"""Return "app_label.model_label.manager_name"."""
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return "%s.%s" % (self.model._meta.label, self.name)
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def __class_getitem__(cls, *args, **kwargs):
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return cls
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def deconstruct(self):
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"""
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Return a 5-tuple of the form (as_manager (True), manager_class,
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queryset_class, args, kwargs).
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Raise a ValueError if the manager is dynamically generated.
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"""
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qs_class = self._queryset_class
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if getattr(self, "_built_with_as_manager", False):
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# using MyQuerySet.as_manager()
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return (
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True, # as_manager
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None, # manager_class
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"%s.%s" % (qs_class.__module__, qs_class.__name__), # qs_class
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None, # args
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None, # kwargs
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)
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else:
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module_name = self.__module__
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name = self.__class__.__name__
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# Make sure it's actually there and not an inner class
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module = import_module(module_name)
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if not hasattr(module, name):
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raise ValueError(
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"Could not find manager %s in %s.\n"
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"Please note that you need to inherit from managers you "
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"dynamically generated with 'from_queryset()'."
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% (name, module_name)
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)
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return (
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False, # as_manager
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"%s.%s" % (module_name, name), # manager_class
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None, # qs_class
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self._constructor_args[0], # args
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self._constructor_args[1], # kwargs
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)
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def check(self, **kwargs):
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return []
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@classmethod
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def _get_queryset_methods(cls, queryset_class):
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def create_method(name, method):
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@wraps(method)
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def manager_method(self, *args, **kwargs):
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return getattr(self.get_queryset(), name)(*args, **kwargs)
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return manager_method
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new_methods = {}
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for name, method in inspect.getmembers(
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queryset_class, predicate=inspect.isfunction
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):
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# Only copy missing methods.
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if hasattr(cls, name):
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continue
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# Only copy public methods or methods with the attribute
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# queryset_only=False.
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queryset_only = getattr(method, "queryset_only", None)
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if queryset_only or (queryset_only is None and name.startswith("_")):
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continue
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# Copy the method onto the manager.
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new_methods[name] = create_method(name, method)
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return new_methods
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@classmethod
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def from_queryset(cls, queryset_class, class_name=None):
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if class_name is None:
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class_name = "%sFrom%s" % (cls.__name__, queryset_class.__name__)
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return type(
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class_name,
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(cls,),
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{
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"_queryset_class": queryset_class,
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**cls._get_queryset_methods(queryset_class),
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},
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)
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def contribute_to_class(self, cls, name):
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self.name = self.name or name
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self.model = cls
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setattr(cls, name, ManagerDescriptor(self))
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cls._meta.add_manager(self)
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def _set_creation_counter(self):
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"""
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Set the creation counter value for this instance and increment the
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class-level copy.
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"""
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self.creation_counter = BaseManager.creation_counter
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BaseManager.creation_counter += 1
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def db_manager(self, using=None, hints=None):
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obj = copy.copy(self)
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obj._db = using or self._db
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obj._hints = hints or self._hints
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return obj
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@property
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def db(self):
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return self._db or router.db_for_read(self.model, **self._hints)
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#######################
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# PROXIES TO QUERYSET #
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#######################
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def get_queryset(self):
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"""
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Return a new QuerySet object. Subclasses can override this method to
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customize the behavior of the Manager.
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"""
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return self._queryset_class(model=self.model, using=self._db, hints=self._hints)
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def all(self):
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# We can't proxy this method through the `QuerySet` like we do for the
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# rest of the `QuerySet` methods. This is because `QuerySet.all()`
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# works by creating a "copy" of the current queryset and in making said
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# copy, all the cached `prefetch_related` lookups are lost. See the
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# implementation of `RelatedManager.get_queryset()` for a better
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# understanding of how this comes into play.
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return self.get_queryset()
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def __eq__(self, other):
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return (
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isinstance(other, self.__class__)
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and self._constructor_args == other._constructor_args
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)
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def __hash__(self):
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return id(self)
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class Manager(BaseManager.from_queryset(QuerySet)):
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pass
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class ManagerDescriptor:
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def __init__(self, manager):
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self.manager = manager
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def __get__(self, instance, cls=None):
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if instance is not None:
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raise AttributeError(
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"Manager isn't accessible via %s instances" % cls.__name__
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)
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if cls._meta.abstract:
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raise AttributeError(
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"Manager isn't available; %s is abstract" % (cls._meta.object_name,)
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)
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if cls._meta.swapped:
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raise AttributeError(
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"Manager isn't available; '%s' has been swapped for '%s'"
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% (
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cls._meta.label,
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cls._meta.swapped,
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)
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)
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return cls._meta.managers_map[self.manager.name]
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class EmptyManager(Manager):
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def __init__(self, model):
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super().__init__()
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self.model = model
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def get_queryset(self):
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return super().get_queryset().none()
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