modeldiffmixin.py

modeldiffmixin.py

from django.forms.models import model_to_dict

class ModelDiffMixin(object):

    def __init__(self, *args, **kwargs):
        super(ModelDiffMixin, self).__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 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(ModelDiffMixin, self).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])

If storing timezone aware datetimes the diff method thinks that the value has changed.

(
  'created_on', 
  (
    datetime.datetime(2021, 3, 28, 15, 25, 51, 156849, tzinfo=<UTC>),  # New value
    datetime.datetime(2021, 3, 28, 18, 25, 51, tzinfo=<DstTzInfo 'Asia/Bahrain' +03+3:00:00 STD>) # Old value
  )
)