获取post_save信号中字段的先前值

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

@receiver(post_save, sender=YourModel)
def your_handler(sender, instance, created, **kwargs):
    if not created:
        # 获取模型实例的先前值
        prev_value = sender.objects.get(id=instance.id).field_name
        
        # 获取模型实例的新值
        new_value = instance.field_name
        
        # 在这里处理先前值和新值的逻辑
        ...