Thanks for the info and pointers Karen, I really appreciate it. I got the feeling this might be a semi-scary way when searching the web for meta and python this afternoon, and didn't really find a lot. I did up screen prototypes for this app, and then designed a db model to accommodate it, and now need to write the python code for the db and the views, etc. That's probably the reverse order a lot of django devs use, but it has worked well for me over the years. And, I always look at the actual db structure and try to reduce wasted space etc. I'll do some re-thinking here - I was actually torn on whether to use subtypes or not. More complicated (bad) but better db space usage (good). I guess disk space is pretty cheap these days lol.
Thanks again, Peter On May 6, 6:25 pm, "Karen Tracey" <[EMAIL PROTECTED]> wrote: > On Tue, May 6, 2008 at 3:01 PM, Peter Bailey <[EMAIL PROTECTED]> wrote: > > > Hey Karen. I used manage.py validate. My model validated before I > > added the abstract class and changed the class signatures. But I > > probably did something silly. Here is a chunk of the code: > > > # will use this for subclassing into our item subtypes > > class AbstractType(models.Model): > > name = models.CharField(max_length=100) > > class Meta: > > abstract = True > > > class Item(models.Model): > > """Item information for survey pages - pages will contain one or > > more of these""" > > sub_item = models.ForeignKey(AbstractType) > > This is the problem: you can't have a ForeignKey to an abstract model. See > this thread: > > http://groups.google.com/group/django-developers/browse_thread/thread... > > particularly Malcolm's reply. As mentioned in that thread, Django's way to > have a ForeignKey "point" to an unknown (or incompletely specified) type is > something called generic relations. Though it might seem (as suggested at > the beginning of that thread) that generic relations could be dropped in > favor of model inheritance, that's not actually the case (as Malcolm > describes). > > Alternatively, perhaps your use case would be better served by non-abstract > inheritance? Inheritance doc is here: > > http://www.djangoproject.com/documentation/model-api/#model-inheritance > > You probably want to give it a careful read and see which way best fits with > they way you are approaching your problem. > > [snipped remainder of model definitions] > > > Well there is some of the model code - thanks for taking a look - I > > think I need to spend a couple of weeks reading 24 hours a day to get > > up to speed on all this technology, But I have just escaped from dot > > niet and asp and sql server etc etc. Oh, what a feeling, what a rush! > > You are rather jumping into the deep end by starting off with inheritance, > which only recently landed in the Django trunk. So there are probably not > that many blog posts or mailing list threads yet with guidance, sample > scenarios, how to use the feature. etc. But if you're comfortable with a > steep learning curve, in the end I expect you will figure it out. Good > luck! > > Karen > > > Cheers > > > On May 6, 2:34 pm, "Karen Tracey" <[EMAIL PROTECTED]> wrote: > > > On Tue, May 6, 2008 at 2:25 PM, Peter Bailey <[EMAIL PROTECTED]> > > wrote: > > > > > Hey alen. I have tried implementing this and it makes good sense as > > > > far as I can see, but when I validate the model I always get an > > > > AttributeError: 'NoneType' object has no attribute 'name'. > > > > How are you validating the model? > > > > I have tried removing name from the definition of the class - same > > > > > message (not sure where it is getting 'name' from since I deleted it. > > > > I also looked around and saw that some other have had similar > > > > problems, and it seemed to be a string definition problem. So I put > > > > back 'name' and changed it to an IntegerField - same unhappy result. > > > > > Do you have any notion of what the problem is? The code looks right to > > > > me. > > > > It sounds like you have some code somewhere that is expecting to always > > be > > > handed an instance of your model, and thus be able to access the field > > > 'name', but it is in fact sometimes getting handed None. When handed > > None, > > > it still tries to access 'name', but since None has no attribute 'name', > > you > > > get the error. If you post the code someone could probably help > > pinpoint > > > the error more specifically. > > > > Karen > > > > > Thanks, > > > > > Peter > > > > > On May 6, 1:33 pm, Peter Bailey <[EMAIL PROTECTED]> wrote: > > > > > Thanks very much for your solution and reply alen. I'm learning the > > > > > ins and outs of python and django at the same time - fun adventure - > > > > > so far python is blowing me away - I love it. Better than anything I > > > > > have used before - 3 assemblers,c, c++ java, vb, ruby, php, asp, etc > > > > > (guess I am dating myself lol - most people don't seem to even ever > > > > > have looked at assembler these days. I used to love it - 7 years of > > > > > that after university) Oh, and of course C was always the bomb too > > :-) > > > > > > Thanks again, > > > > > > Peter > > > > > > On May 6, 12:46 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> > > > > > wrote: > > > > > > > Define a 'abstract' attribute of Meta inner class and set it to > > true > > > > > > like so: > > > > > > > class AbstractType(models.Model): > > > > > > name = models.CharField(max_length=100) > > > > > > > class Meta: > > > > > > abstract = True > > > > > > > class RadioBoxTypes(AbstractType): > > > > > > radio_lable = models.CharField(max_length=20) > > > > > > > Regards, > > > > > > -Alen > > > > > > > On May 6, 5:43 pm, Peter Bailey <[EMAIL PROTECTED]> wrote: > > > > > > > > I have designed a small db model (on paper) and want to > > implement it > > > > > > > in my models.py file. So far, this has been pretty straight > > forward, > > > > > > > but I have a generic superclass and several subclasses, and I am > > > > > > > unsure how to implement this. > > > > > > > > My DB has page objects (webpages) with a few common attributes, > > and > > > > a > > > > > > > fk to an Item object. The item object is the generic superclass. > > It > > > > > > > could be a RadioType, a CheckBoxType, a VerbatimType, etc. These > > all > > > > > > > have attributes specific to themselves. > > > > > > > > Anyway, I don't grok how to set up this type of relationship in > > my > > > > > > > models.py file. Is there a standard way of doing this, or does > > > > anyone > > > > > > > have an suggestions or can point me to some relevant info? > > > > > > > > e.g. Pages - pointed to by fk in Items > > > > > > > ---------- > > > > > > > > Items - has key to one of the below > > > > > > > -------- > > > > > > > > RadioBoxTypes CheckboxTypes VerbatimTypes etc > > > > > > > ----------------------- ----------------------- > > > > > > > --------------------- ---- > > > > > > > > Thanks very much. Sorry if this is a dumb question - always fun > > > > being > > > > > > > a newbie :-( > > > > > > > > Peter --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. 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