fetching not with custom primary id in django

I have created a table in which the primary id have to customize id product_id like

class Product(models.Model):
    
    product_id = models.BigIntegerField(auto_created = True,primary_key = True, unique=True)
    name = models.CharField(max_length=200)
    ref = models.CharField(max_length=100)
    number= models.CharField(max_length=100)
    
    class Meta:
        db_table = "products"

    def __str__(self):
        return self.name

after creating the record I want to get the id of the latest record but when I retrieve the data with this id getting None

product = Product.objects.create(name=name, ref=ref, number=number)
print(product.product_id)

product.product_id id getting null Pleae give me a solution to why this is happening.

Django will set the primary key of an AutoField or BigAutoField, given that the database supports returning the assigned primary key.

You thus should rewrite the model to:

class Product(models.Model):
    product_id = models.BigAutoField(primary_key=True)
    # …