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1import logging
2from typing import Optional, TYPE_CHECKING, Any, Sequence
4logger = logging.getLogger(__name__)
7class CachedFieldsMixin:
8 """
9 Cached fields mixin. Usage:
10 1) List cached field names in cached_fields list
11 2) Implement get_xxx functions where xxx is cached field name
12 3) Call update_cached_fields() to refresh
13 4) Optionally call update_cached_fields_pre_save() on pre_save signal for objects (to automatically refresh on save)
14 """
16 cached_fields: Sequence[str] = []
18 if TYPE_CHECKING:
19 pk: Any = None
21 def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
22 pass
24 def update_cached_fields(
25 self, commit: bool = True, exceptions: bool = True, updated_fields: Optional[Sequence[str]] = None
26 ):
27 """
28 Updates cached fields using get_xxx calls for each cached field (in cached_fields list).
29 :param commit: Save update fields to DB
30 :param exceptions: Raise exceptions or not
31 :param updated_fields: List of cached fields to update. Pass None for all cached fields.
32 """
33 try:
34 fields = updated_fields or self.cached_fields
35 for k in fields:
36 f = "get_" + k
37 if not hasattr(self, f):
38 raise Exception(
39 "Field {k} marked as cached in {obj} but function get_{k}() does not exist".format(
40 k=k, obj=self
41 )
42 )
43 v = self.__getattribute__(f)()
44 setattr(self, k, v)
45 if commit:
46 self.save(update_fields=fields) # pytype: disable=attribute-error
47 except Exception as e:
48 logger.error("%s.update_cached_fields: %s", self.__class__, e)
49 if exceptions:
50 raise e
52 def update_cached_fields_pre_save(self, update_fields: Optional[Sequence[str]]):
53 """
54 Call on pre_save signal for objects (to automatically refresh on save).
55 :param update_fields: list of fields to update
56 """
57 if hasattr(self, "pk") and self.pk and update_fields is None:
58 self.update_cached_fields(commit=False, exceptions=False)
61def update_cached_fields(*args):
62 """
63 Calls update_cached_fields() for each object passed in as argument.
64 Supports also iterable objects by checking __iter__ attribute.
65 :param args: List of objects
66 :return: None
67 """
68 for a in args:
69 if a is not None:
70 if hasattr(a, "__iter__"):
71 for e in a:
72 e.update_cached_fields()
73 else:
74 a.update_cached_fields()