fetching not with custom primary id in django-CodePudding

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.

CodePudding user response：

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)
    # …

CodePudding user response：

The reason for this is that Django does not know what the primary key (pk) of the object is going to be before the object is saved in the database.

That is because Django does not determine the value of the pk for the incoming object, your database does. In order to get the pk, you first have to save the object then retrive its pk.