241 lines
8.5 KiB
Python
241 lines
8.5 KiB
Python
from django.db.models import QuerySet
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from django.db.models.expressions import BaseExpression, Combinable
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from django.db.models.query import ValuesIterable
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from django.db.models.manager import Manager
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"""
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Base Idea:
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- to have a queryset function that easily allows you to build some sort of "pure class" in a queryset.
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- make it able to seamlessly use annotation functions
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- allow callback modication of data, which is needed if your dataclass is frozen.
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By default the PureManager and PureQuerySet will use PureDataclass as handler, expecting your pureclass to be a dataclasses.dataclass type.
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An Example:
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@dataclass
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class MyClass
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id: int
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some_relation: str
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next_id: int
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SomeModel.objects.filter(...).exclude(...).purify(MyClass, some_relation=F('some__model__relation'), next_id=Lambda(lambda x: x.get('id')+1))
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This allows you to move an iterator into another layer, where it either can be consumed, or used as an input for another queryset call,
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but still guaranteeing, that regular usage of the iterator will not yield any smart object.
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It is good if you want to build a best-of-both-worlds approach for subquery-capable repository pattern, which is one of the biggest issues if you want
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to keep your business logic out of the repo layer, but still want to utilize djangos queryset mechanics properly.
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"""
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## Useful for queryset function purify()
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class BaseLeap:
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skip = False # if skip is true, this leap will not be actually processed.
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resolves_field = True # if resolves_field is true, this leap will be called for a single field with resolve()
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post_processing = False # if post_processing is true, this leap will in the end be called with dbdata, and be able to manipulate the whole dictionary.
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def resolve(self, model, dbdata):
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raise NotImplementedError
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def post_process(self, model, dbdata):
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raise NotImplementedError
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class Leap(BaseLeap):
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""" value function that leaps SQL handling. """
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def __init__(self, value=None):
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self.value = value
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def resolve(self, model, dbdata):
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return self.value
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class Lambda(Leap):
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""" leap value that calls a lambda expression. """
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def __init__(self, callback):
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self.callback = callback if callable(callback) else None
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def resolve(self, model, dbdata):
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# at this point i could check if callback needs 0-2 arguments and decide the call.
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if self.callback:
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return self.callback(dbdata)
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class Skip(BaseLeap):
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""" Skips this key from being retrieved from the database or used in the dataclass instantiation """
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skip = True
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resolves_field = False
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class Callback(BaseLeap):
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resolves_field = False
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post_processing = True
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def __init__(self, callback):
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self.callback = callback
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def post_process(self, model, dbdata):
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if self.callback:
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return self.callback(dbdata)
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## Wrapper to handle some sort of pure baseclass
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class PureHandler:
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""" handler for a pure baseclass
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defines how a pureclass can be created, and how to retrieve all field names, and the required ones.
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"""
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@classmethod
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def wrap(cls, klass):
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return cls(klass)
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def __init__(self, klass):
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self.klass = klass
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def create(self, **kwargs):
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return self.klass(**kwargs)
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def get_field_names(self):
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return self.klass.__dict__.keys()
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@property
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def pureclass(self):
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return self.klass
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@property
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def required_keys(self):
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return self.get_field_names()
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class PureDict(PureHandler):
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""" PureHandler that outputs a dictionary """
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def __init__(self, klass=None):
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# it is not required to define dict, but you could do OrderedDict e.g.
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self.klass = klass or dict
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def get_field_names(self):
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# dictionary has no required fields.
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return []
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class PureDataclass(PureHandler):
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""" handles dataclasses.dataclass derivatives """
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def create(self, **kwargs):
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# clean field names to be only valid if they are on the dataclass.
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pure_fields = self.get_field_names()
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kwargs = {k: v for k, v in kwargs.items() if k in pure_fields}
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return self.klass(**kwargs)
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def get_field_names(self):
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return list(self.klass.__dataclass_fields__.keys())
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# @TODO: PurePydantic
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###### QuerySet Plugin.
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class PureIterable(ValuesIterable):
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"""
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Iterable returned by purify() that yields a pure class for each row.
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Replaces the standard iterable of the queryset.
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"""
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def __iter__(self):
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queryset = self.queryset
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model = self.queryset.model
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query = queryset.query
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compiler = query.get_compiler(queryset.db)
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pure_data = getattr(queryset, '_pureclass_extra', {})
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pure_handler = queryset._pureclass
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# extra(select=...) cols are always at the start of the row.
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names = [
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*query.extra_select,
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*query.values_select,
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*query.annotation_select,
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]
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indexes = range(len(names))
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for row in compiler.results_iter(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size):
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dbdata = {names[i]: row[i] for i in indexes}
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# post-processors will be able to rewrite the whole dictionary.
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post_processors = []
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# we overwrite db data bluntly for now. actually we would provide callbacks the current dict.
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for k, v in pure_data.items():
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if v.resolves_field:
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dbdata[k] = v.resolve(model, dbdata)
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if v.post_processing:
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post_processors.append(v)
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if post_processors:
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for processor in post_processors:
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processed = processor.post_process(model, dbdata)
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if processed is not None:
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dbdata = processed
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yield pure_handler.create(**dbdata)
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class PureQuerySetMixin:
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_pureclass_handler = PureDataclass
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def purify(self, *args, **kwargs):
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"""
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generates pure objects
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Acts like values(), however:
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- first argument is a pureclass or purehandler, if not a string.
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- if pureclass is not defined in purify, you have to define it on the queryset, or the model, with _pureclass,
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otherwise it will raise a RuntimeError.
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- keyword arguments of type "Leap" are used as deferred values, and resolved independently.
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- values() is called with every required_key on the dataclass not handled by a Leap
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"""
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if len(args) and not isinstance(args[0], str):
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# we assume this is our dataclass
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# @TODO better checks.
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handler = args[0]
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args = args[1:]
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else:
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# determine dataclass.
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handler = getattr(self, '_pureclass', getattr(self.model, '_pureclass', None))
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if not handler:
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raise RuntimeError("Trying to purify a class without destination class.")
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if not isinstance(handler, PureHandler):
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handler = self._pureclass_handler.wrap(handler)
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all_keys = [*args, *kwargs.keys()]
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unhandled_keys = list(set(handler.required_keys) - set(all_keys))
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args = [*args, *unhandled_keys]
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new_kw = {}
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extra = {}
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for k, v in kwargs.items():
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if isinstance(v, Leap):
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if not v.skip:
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extra[k] = v
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elif isinstance(v, BaseExpression) or isinstance(v, Combinable):
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new_kw[k] = v
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else:
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new_kw[k] = v
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# copy ourself with values() and save the results on the cloned queryset.
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values = self.values(*args, **new_kw)
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values._iterable_class = PureIterable
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values._pureclass_extra = extra
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values._pureclass = handler
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return values
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class PureQuerySet(PureQuerySetMixin, QuerySet):
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# overwrite cloning.
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def _clone(self):
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c = super()._clone()
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for key in ['_pureclass', '_pureclass_extra', '_pureclass_handler']:
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if hasattr(self, key):
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setattr(c, key, getattr(self, key))
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return c
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# i use a mixin instead for better clarity. purify is completely safe, as it does not call _chain.
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# however you can also simply do:
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#class PureManager(BaseManager.from_queryset(PureQuerySet)):
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# pass
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class PureManager(PureQuerySetMixin, Manager):
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def get_queryset(self):
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return PureQuerySet(self.model, using=self._db)
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