Tom, Thanks for the quick reply! However, when I tried that I got an error saying that inventoryitem "is an invalid keyword argument for this function". I fixed this by manually specifying the OneToOneField relationship with the parent class as inventoryItem and setting parent_link=True. With that in place, I get errors about InventoryItem fields not being allowed to be null within InventoryBook. This doesn't make sense to me since InventoryBook should only have a link to the parent and its own local book-specific fields - not the fields previously declared in the parent InventoryItem. I have not declared any models to be abstract (and in fact have not declared Meta: at all).
If I need to manually specify all of the InventoryItem fields again in the constructor of the InventoryBook, I can. But doing so seems to defeat the purpose of using inheritance to begin with. Is there something I'm still overlooking? Thanks again, -Alex On Oct 28, 5:53 am, Tom Evans <tevans...@googlemail.com> wrote: > On Fri, Oct 28, 2011 at 7:50 AM, Alex <alexc...@gmail.com> wrote: > > I've been scouring Google and the Django documentation and I can't > > figure out how to do this. I'm working on an inventory management > > system for my shop. My inventory models.py similar to the following: > > > class ItemType( models.Model ): > > def __unicode__( self ): > > return "blah blah blah" > > > itemType = models.CharField( max_length = 32 ) > > isBook = models.BooleanField() > > > class InventoryItem( models.Model ): > > def __unicode__( self ): > > return "blah" > > > itemType = models.ForeignKey( ItemType ) > > description = models.CharField( max_length = 256 ) > > > class InventoryBook( InventoryItem ): > > def __unicode__( self ): > > return "blah blah" > > > title = models.CharField( max_length = 64 ) > > > In my web app, I create a ModelForm based on InventoryItem and present > > that to the user. Upon submission, the POST data is used to create an > > instance of InventoryItem. I then check to see if > > inventoryItem.itemType.isBook() is True - if True, I want to cast > > inventoryItem to an InventoryBook type so I can set the extra fields > > and call save() so that it creates records in both tables in the MySQL > > database. > > > I started trying to add a method to InventoryItem that would return an > > InventoryBook instance after being given the title string, but that > > doesn't work because Python doesn't have prototyping/forward > > declarations. > > > Am I approaching this completely wrong, or am I just overlooking > > something simple? Any advice or links to relevant documentation would > > be *much* appreciated. Thanks! > > > -Alex > > If you have an InventoryItem which should be an InventoryBook, you > need to create the InventoryBook, not cast to it. > > item = … > if item.itemType.isBook(): > book = InventoryBook.objects.create(inventoryitem=item, title=…) > > Inheritance like this in django isn't really like OOO inheritance, > InventoryBook just magically gains a OneToOneField back to > InventoryItem called inventoryitem. > > Cheers > > Tom -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
