Save a model instance with a non-existent field

Question

I don't know if this is a bug or Django just allows it to happen. I have a Django model:

class Author(models.Model):
    name = models.CharField(max_length=128)

I create an instance of it and assign a value to a non-existent field address:

author = Author()
author.name = 'abce'
author.address = 'defg'
author.save()

The instance is saved successfully and there is no error messages. Is this normal?

score 1 · Accepted Answer · answered Nov 30 '16 at 09:18

Yes its normal, The address never actually gets saved and if you were to reference this object again, it wouldn't be there. Its just that Python qwerk that you are allowed to add fields to an object instance whenever you want

class A:
    pass
a = A()
a.foo = 1

_{Whether or not you should is a different matter...}

score 1 · Answer 2 · edited May 23 '17 at 12:02

1

In Python, user-defined types are generally mutable, which means they can be altered, and adding an attribute to a user-defined object is just like adding a key to an ordinary dictionary. You can check this answer for more details are user defined classes mutable

edited May 23 '17 at 12:02

Community

1
1

answered Nov 30 '16 at 09:30

ettanany

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score 1 · Answer 3 · answered Nov 30 '16 at 09:31

Yeah Normal. Django will do update only for the field you defined

From django code

    for field in self._meta.concrete_fields:
        if field.attname in non_loaded_fields:
            # This field wasn't refreshed - skip ahead.
            continue
        setattr(self, field.attname, getattr(db_instance, field.attname))

You can see fields by

Author()._meta.concrete_fields

But you cannot do this like

Author(name="name", address="sss")

It will raise invalid argument.

Save a model instance with a non-existent field

3 Answers3