如何在普通形式的模型中模拟upload_to函数

from django.db import models

def upload_to(instance, filename):
    # 自定义上传路径和文件名
    return 'uploads/{0}/{1}'.format(instance.id, filename)

class MyModel(models.Model):
    file = models.FileField(upload_to=upload_to)

from django.db import models

def custom_upload_to(instance, filename):
    # 自定义上传路径和文件名
    return 'custom_uploads/{0}/{1}'.format(instance.id, filename)

class MyModel(models.Model):
    file = models.FileField(upload_to=custom_upload_to)

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

def custom_upload_to(instance, filename):
    # 自定义上传路径和文件名
    return 'custom_uploads/{0}/{1}'.format(instance.id, filename)

class MyModel(models.Model):
    file = models.FileField(upload_to='')

def pre_save_model(sender, instance, **kwargs):
    if not instance.file:
        # 生成文件路径并赋值给模型字段
        instance.file = custom_upload_to(instance, instance.file.name)

pre_save.connect(pre_save_model, sender=MyModel)