id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
28019	Django django.db.models.Model.save() logic bit illogical?	Jacek Kałucki	nobody	"In code below, calling “Foo(name='Foo Bar').save()” method raises ValueError “Cannot force an update in save() with no primary key” - let’s check what goes wrong here:
1) I didn’t pass any parameters so why logic mentions about “force” and “update” since I’m not forcing nor updating but inserting new data row? I’ve figured out that logic adds fields to “update_fields” parameters itself and in this case it’s a “name” which is class Foo property name.
It won’t happened if there is no class inheritance scenario. Why? But it leads us to the next point.
2) Let’s check when the “not pk_set and (force_update or update_fields)” condition is fulfilled.
IMHO if “pk_set” is false there is no need to check “update_fields” because it’s never used in this scenario, it may be used only in case of “pk_set” equals true but these states are mutually exclusive.

My proposal is to revise “get_deferred_fields()” method to handle class attributes correctly in case of inheritance and remove redundant “update_fields” checking on inserts.

{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!python
class Bar(models.Model):

    name = models.CharField(max_length=100, blank=True)


class Foo(Bar):

    first_name = models.CharField(max_length=50, blank=True)
    last_name = models.CharField(max_length=50, blank=True)

    def __init__(self, *args, **kwargs):
        name = kwargs.get('name')
        if name:
            (first_name, last_name) = name.split()
            kwargs['first_name'] = first_name
            kwargs['last_name'] = last_name
        super(Foo, self).__init__(*args, **kwargs)

    @property
    def name(self):
        names = (self.first_name, self.last_name)
        return "" "".join(x for x in names if x)

    @name.setter
    def name(self, value):
        (self.first_name, self.last_name) = value.split()
  }}}
}}}"	Bug	closed	Database layer (models, ORM)	1.10	Normal	needsinfo			Unreviewed	0	0	0	0	0	0