One piece of code I use in pretty much every project is a
ModelDiffMixin class. I’m not sure where I first found it, I think it was this answer on stackoverflow. Here it is in full glory:
from django.forms.models import model_to_dict class ModelDiffMixin: """ A model mixin that tracks model fields' values and provides some useful api to know what fields have been changed. """ def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs) self.__initial = self._dict @property def diff(self): d1 = self.__initial d2 = self._dict diffs = [(k, (v, d2[k])) for k, v in d1.items() if v != d2[k]] return dict(diffs) @property def has_changed(self): return bool(self.diff) @property def changed_fields(self): return list(self.diff.keys()) def get_field_diff(self, field_name): """ Returns a diff for field if it's changed and None otherwise. """ return self.diff.get(field_name, None) def save(self, *args, **kwargs): """ Saves model and set initial state. """ super().save(*args, **kwargs) self.__initial = self._dict @property def _dict(self): return model_to_dict(self, fields=[field.name for field in self._meta.fields])
There are multiple versions of it on the internet. For example this one includes a fix for float values.
So simple yet so useful.