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
17761	save_base() does not properly detect when MTI parent key is unset	Aron Grififs	nobody	"Consider the following MTI scenario, where the primary key of the parent is a !CharField:

{{{
#!python

from django.db import models

class Foo(models.Model):
    id = models.CharField(max_length=6, primary_key=True)

class Bar(Foo):
    data = models.TextField()
}}}

Attempting to instantiate and save the child model fails:

{{{
>>> from bar.models import Bar
>>> b=Bar()
>>> b.pk='abcdef'
>>> b.save()
Traceback (most recent call last):
  File ""<console>"", line 1, in <module>
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/models/base.py"", line 460, in save
    self.save_base(using=using, force_insert=force_insert, force_update=force_update)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/models/base.py"", line 553, in save_base
    result = manager._insert(values, return_id=update_pk, using=using)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/models/manager.py"", line 195, in _insert
    return insert_query(self.model, values, **kwargs)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/models/query.py"", line 1436, in insert_query
    return query.get_compiler(using=using).execute_sql(return_id)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/models/sql/compiler.py"", line 791, in execute_sql
    cursor = super(SQLInsertCompiler, self).execute_sql(None)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/models/sql/compiler.py"", line 735, in execute_sql
    cursor.execute(sql, params)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/backends/util.py"", line 34, in execute
    return self.cursor.execute(sql, params)
  File ""/home/aron/.virtualenvs/pp/lib/python2.7/site-packages/django/db/backends/sqlite3/base.py"", line 234, in execute
    return Database.Cursor.execute(self, query, params)
IntegrityError: bar_bar.foo_ptr_id may not be NULL
}}}

The reason this happens is the following code around line 500 in
[source:django/trunk/django/db/models/base.py db/models/base.py]:

{{{
#!python
class Model(object):
    ...

    def save_base(...):
        ...

        for parent, field in meta.parents.items():
            # At this point, parent's primary key field may be unknown
            # (for example, from administration form which doesn't fill
            # this field). If so, fill it.
            if field and getattr(self, parent._meta.pk.attname) is None and getattr(self, field.attname) is not None:
                setattr(self, parent._meta.pk.attname, getattr(self, field.attname))

            self.save_base(cls=parent, origin=org, using=using)
}}}

This fails because the default value for a !CharField is the emtpy string
rather than None. This code works for an !IntegerField primary key (which
defaults to None until set).  It also works for a !CharField(null=True) but
it's not clear to me that's the right answer, because it means null is
valid for the DB column, which isn't right.

I ''think'' the right answer is to change the test from ""is None"" to ""in
[None, !'']"" as shown in the attached patch.

You might ask, ""What about the test on the child model's pk? Does that need
to change too?"" The answer is no, because the child model's pk is a
!OneToOneField which defaults to None, so only the first None-test on the
line needs to change.
"	Bug	closed	Database layer (models, ORM)	1.3	Normal	fixed		aron@…	Accepted	1	0	0	1	0	0