first comit

venv/lib/python3.10/site-packages/django/db/models/fields/mixins.py

@@ -0,0 +1,59 @@
+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