from django.core import checks NOT_PROVIDED = object() class FieldCacheMixin: """Provide an API for working with the model's fields value cache.""" def get_cache_name(self): raise NotImplementedError def get_cached_value(self, instance, default=NOT_PROVIDED): cache_name = self.get_cache_name() try: return instance._state.fields_cache[cache_name] except KeyError: if default is NOT_PROVIDED: raise return default def is_cached(self, instance): return self.get_cache_name() in instance._state.fields_cache def set_cached_value(self, instance, value): instance._state.fields_cache[self.get_cache_name()] = value def delete_cached_value(self, instance): del instance._state.fields_cache[self.get_cache_name()] class CheckFieldDefaultMixin: _default_hint = ('<valid default>', '<invalid default>') def _check_default(self): if self.has_default() and self.default is not None and not callable(self.default): return [ checks.Warning( "%s default should be a callable instead of an instance " "so that it's not shared between all field instances." % ( self.__class__.__name__, ), hint=( 'Use a callable instead, e.g., use `%s` instead of ' '`%s`.' % self._default_hint ), obj=self, id='fields.E010', ) ] else: return [] def check(self, **kwargs): errors = super().check(**kwargs) errors.extend(self._check_default()) return errors