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.