最好的方法是使用pre_save信号。在09年这个问题被提出并回答的时候，可能还没有这个选项，但今天看到这个问题的人应该这样做:

@receiver(pre_save, sender=MyModel)
def do_something_if_changed(sender, instance, **kwargs):
    try:
        obj = sender.objects.get(pk=instance.pk)
    except sender.DoesNotExist:
        pass # Object is new, so field hasn't technically changed, but you may want to do something else here.
    else:
        if not obj.some_field == instance.some_field: # Field has changed
            # do something

最好的方法是使用pre_save信号。在09年这个问题被提出并回答的时候，可能还没有这个选项，但今天看到这个问题的人应该这样做:

@receiver(pre_save, sender=MyModel)
def do_something_if_changed(sender, instance, **kwargs):
    try:
        obj = sender.objects.get(pk=instance.pk)
    except sender.DoesNotExist:
        pass # Object is new, so field hasn't technically changed, but you may want to do something else here.
    else:
        if not obj.some_field == instance.some_field: # Field has changed
            # do something

有一个属性__dict__，它将所有字段作为键，并将值作为字段值。所以我们可以比较其中两个

只需将模型的save函数更改为下面的函数即可

def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
    if self.pk is not None:
        initial = A.objects.get(pk=self.pk)
        initial_json, final_json = initial.__dict__.copy(), self.__dict__.copy()
        initial_json.pop('_state'), final_json.pop('_state')
        only_changed_fields = {k: {'final_value': final_json[k], 'initial_value': initial_json[k]} for k in initial_json if final_json[k] != initial_json[k]}
        print(only_changed_fields)
    super(A, self).save(force_insert=False, force_update=False, using=None, update_fields=None)

使用示例:

class A(models.Model):
    name = models.CharField(max_length=200, null=True, blank=True)
    senior = models.CharField(choices=choices, max_length=3)
    timestamp = models.DateTimeField(null=True, blank=True)

    def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
        if self.pk is not None:
            initial = A.objects.get(pk=self.pk)
            initial_json, final_json = initial.__dict__.copy(), self.__dict__.copy()
            initial_json.pop('_state'), final_json.pop('_state')
            only_changed_fields = {k: {'final_value': final_json[k], 'initial_value': initial_json[k]} for k in initial_json if final_json[k] != initial_json[k]}
            print(only_changed_fields)
        super(A, self).save(force_insert=False, force_update=False, using=None, update_fields=None)

产生只包含已更改字段的输出

{'name': {'initial_value': '1234515', 'final_value': 'nim'}, 'senior': {'initial_value': 'no', 'final_value': 'yes'}}

有时我想检查多个共享这些字段的模型上相同特定字段的更改，因此我定义了这些字段的列表并使用一个信号。在这种情况下，只有当某些东西发生了变化，或者条目是新的时，地理编码才会寻址:

from django.db.models.signals import pre_save
from django.dispatch import receiver

@receiver(pre_save, sender=SomeUserProfileModel)
@receiver(pre_save, sender=SomePlaceModel)
@receiver(pre_save, sender=SomeOrganizationModel)
@receiver(pre_save, sender=SomeContactInfoModel)
def geocode_address(sender, instance, *args, **kwargs):

    input_fields = ['address_line', 'address_line_2', 'city', 'state', 'postal_code', 'country']

    try:
        orig = sender.objects.get(id=instance.id)
        if orig:
            changes = 0
            for field in input_fields:
                if not (getattr(instance, field)) == (getattr(orig, field)):
                    changes += 1
            if changes > 0:
                # do something here because at least one field changed...
                my_geocoder_function(instance)
    except:
        # do something here because there is no original, or pass.
        my_geocoder_function(instance)

只编写一次并使用“@receiver”附加当然胜过重写多个模型保存方法，但也许其他人有更好的想法。

我对@iperelivskiy的解决方案的看法是:在大规模的情况下，为每个__init__创建_initial字典是昂贵的，而且大多数时候是不必要的。我稍微改变了mixin，这样它只在你显式地告诉它这样做(通过调用instance.track_changes)时才记录更改:

from typing import KeysView, Optional
from django.forms import model_to_dict

class TrackChangesMixin:
    _snapshot: Optional[dict] = None

    def track_changes(self):
        self._snapshot = self.as_dict

    @property
    def diff(self) -> dict:
        if self._snapshot is None:
            raise ValueError("track_changes wasn't called, can't determine diff.")
        d1 = self._snapshot
        d2 = self.as_dict
        diffs = [(k, (v, d2[k])) for k, v in d1.items() if str(v) != str(d2[k])]
        return dict(diffs)

    @property
    def has_changed(self) -> bool:
        return bool(self.diff)

    @property
    def changed_fields(self) -> KeysView:
        return self.diff.keys()

    @property
    def as_dict(self) -> dict:
        return model_to_dict(self, fields=[field.name for field in self._meta.fields])

注意，字段更改跟踪在django-model-utils中是可用的。

https://django-model-utils.readthedocs.org/en/latest/index.html