Derived model filefield not available - django

Question

I have a base model and derived model from it. base model is not abstract, so it also has table associated with it.
Problem : I create a base instance first and then derived instance. And associate derived instance to base. But I get FileField in my derived class as None, even if its saved and available in parent. Why so? Am I missing something?
Some sample code:
def get_filepath(instance):
return u''+instance.name
def BaseModel(models.Model):
name = models.CharField(max_length=50)
filepath = models.FileField(upload_to=get_filepath,
max_length=255, null=True)
#some other fields
def DerivedModel(BaseModel):
type = models.CharField(max_length=50, null=True, blank=True)
Sample on django shell:
>>> obj = BaseModel.objects.create(name='y')
>>> obj.id
56
>>> obj.save()
>>> obj.id
56
>>> nf=ContentFile("this is dummy text")
>>> obj.filepath.save('dummyfile', nf)
>>> dobj=DerivedModel()
>>> dobj.basemodel_ptr=obj
>>> dobj.save()
>>> dobj.id
56
>>> dobj.filepath
<FieldFile: None>
>>> obj.filepath
<FieldFile: y>
Update: for #dgel's answer:
save_base() does it save the derived object? dobj does not get id after that.
After dobj.save(), it seems attributes in base class are getting overwritten by attributes in derived class.
I added ctime created time in BaseModel with default datetime.datetime.utcnow. So once I save derived object, ctime is updated to save time of derived object.
When I look at the DB through sqlitebrowser, filepath field of the BaseModel row is empty.
>>> dobj.save_base(raw=True)
>>> dobj.id
>>> dobj.save()
>>> dobj.filepath
<FieldFile: None>
>>> obj.ctime
datetime.datetime(2012, 8, 23, 8, 50, 3, 171573)
>>> dobj.ctime
datetime.datetime(2012, 8, 23, 8, 51, 9, 946434)
>>> newdobj = DerivedModel.objects.get(id=dobj.id)
>>> newdobj.ctime
datetime.datetime(2012, 8, 23, 8, 51, 9, 946434)
Thanks.

Answer 1

Try this:
dobj = DerivedModel()
dobj.basemodel_ptr=obj
dobj.save_base(raw=True)