object has no attribute '_state'

[jcage]

Hi everyone. I'm quite new to python and django. I was wondering if
anyone could shed some light on this topic :

My models.py contains the classes QuestionSet and Question, which
inherits the former.
In the shell, I define a Question object as follows

q1 = Question(script = "How are you?", comment = "no comment", order =
1)


but an attempt to run q1.save() results in the following error :

>>> q1.save()
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/Library/Frameworks/Python.framework/Versions/2.6/lib/
python2.6/site-packages/django/db/models/base.py", line 435, in save
self.save_base(using=using, force_insert=force_insert,
force_update=force_update)
File "/Library/Frameworks/Python.framework/Versions/2.6/lib/
python2.6/site-packages/django/db/models/base.py", line 447, in
save_base
using = using or router.db_for_write(self.__class__,
instance=self)
File "/Library/Frameworks/Python.framework/Versions/2.6/lib/
python2.6/site-packages/django/db/utils.py", line 133, in _route_db
return hints['instance']._state.db or DEFAULT_DB_ALIAS
AttributeError: 'Question' object has no attribute '_state'



The class definitions are :

class QuestionSet(models.Model):
title = models.CharField(max_length=100)
description = models.TextField()
order = models.IntegerField()

def __init__(self, *args, **kwargs):
self.title = kwargs.get('title','Default Title')
self.description = kwargs.get('description', 'DefDescription')
self.order = kwargs.get('order', 0)


class Question(QuestionSet):
script = models.CharField(max_length=200)
comment = models.TextField()


def __init__(self, *args, **kwargs):
QuestionSet.__init__(self, args, kwargs)
self.script = kwargs.get('script', "undefined")
self.comment = kwargs.get('comment', "no comment")




Would greatly appreciate any suggestions

[Tom Evans]

You aren't calling the django.db.models.Model constructor on either of
your derived classes. When you write a derived class, be sure to call
the super class constructor:

class MyModel(Model):
def __init__(self, *args, **kwargs):
super(MyModel, self).__init__(*args, **kwargs)

Cheers

Tom

[Demian Brecht]

>> class QuestionSet(models.Model):
>> title = models.CharField(max_length=100)
>> description = models.TextField()
>> order = models.IntegerField()
>>
>> def __init__(self, *args, **kwargs):
>> self.title = kwargs.get('title','Default Title')
>> self.description = kwargs.get('description', 'DefDescription')
>> self.order = kwargs.get('order', 0)

One thing that looks suspect to me here is that you're not calling
__init__ on models.Model.

def __init__(self, *args, **kwargs):
models.Model.__init__(self, ...)

Which will prevent the base class from initializing.

For example:

>>> class A(object):
... def __init__(self):
... print 'A init'
...
>>> class B(A):
... def __init__(self):
... A.__init__(self)
... print 'B init'
...
>>> class C(A):
... def __init__(self):
... print 'C init'
...
>>> C()
C init
<__main__.C object at 0x7fd811c23bd0>
>>> B()
A init
B init
<__main__.B object at 0x7fd811c23c50>

Constructor calls don't bubble up on their own, you have to explicitly
call them.

I would assume that something in the model's base class is what adds the
_state attribute. By short circuiting the constructor, you're preventing
this from ever happening.

--
Demian Brecht
@demianbrecht
http://demianbrecht.github.com

[Tom Evans]

On Fri, Oct 5, 2012 at 3:56 PM, Demian Brecht <demian...@gmail.com> wrote:
>
>>> class QuestionSet(models.Model):
>>> title = models.CharField(max_length=100)
>>> description = models.TextField()
>>> order = models.IntegerField()
>>>
>>> def __init__(self, *args, **kwargs):
>>> self.title = kwargs.get('title','Default Title')
>>> self.description = kwargs.get('description', 'DefDescription')
>>> self.order = kwargs.get('order', 0)
>
>
> One thing that looks suspect to me here is that you're not calling __init__
> on models.Model.
>

I'm sure the OP from June 2010 will be pleased that his question has
been answered so many times…

Cheers

Tom

PS: To call the parent class(es) constuctor(s) correctly when using
python "new style" classes (ie: all Django classes and classes derived
from Django classes), you should use super(ClassName, self).__init__()
and not call the base class directly.

[Demian Brecht]

I'm sure the OP from June 2010 will be pleased that his question has
been answered so many times…

 

Eek, guess I should have read the posting date.

 

PS: To call the parent class(es) constuctor(s) correctly when using
python "new style" classes (ie: all Django classes and classes derived
from Django classes), you should use super(ClassName, self).__init__()
and not call the base class directly.

Call me paranoid: https://fuhm.net/super-harmful/ 

[Tom Evans]

On Fri, Oct 5, 2012 at 6:13 PM, Demian Brecht <demian...@gmail.com> wrote:
> Call me paranoid: https://fuhm.net/super-harmful/

One guys (well publicized) internet rant on why he dislikes super does
not necessarily mean he is correct. Even if he is, follow his own
advice:

Subclasses must use super if their superclasses do

Django's model classes all use super, so should you when defining
subclasses derived from them.

Cheers

Tom

[Demian Brecht]

On 12-10-09 02:12 AM, Tom Evans wrote:
> On Fri, Oct 5, 2012 at 6:13 PM, Demian Brecht <demian...@gmail.com> wrote:
>> Call me paranoid: https://fuhm.net/super-harmful/
>
> One guys (well publicized) internet rant on why he dislikes super does
> not necessarily mean he is correct. Even if he is, follow his own
> advice:
>
> Subclasses must use super if their superclasses do

Good catch, thanks.. Although now I'm interested as to *why* the
resulting behavior is as detailed in the blog..