hey david,
ah - thanks so much! i made two mistakes: using abstract - and
linking to self rather than to Node. i'm guessing here - butu are two
models/tables created and linked together rather than a single 'uber'
table?
anyway, i'm back up and running on my fledgling project - thanks to
you! :-)
-p
On Oct 7, 6:23 pm, David Hall <[EMAIL PROTECTED]> wrote:
> Hi Paul,
>
> So long as the common model is not abstract, it should work. Also, the
> common model must be the one that contains the parent field, and it
> should link to "Node" and not "self".
>
> Using my first example, you should be able to traverse the tree using
> Node.parent and Node.children. Traversing the tree using Job.parent,
> Job.children, Shot.parent or Shot.children will not work.
>
> I've implemented the first example in one of my own apps, and it does
> work! :P
>
> David.
>
>
>
> paul wrote:
> > hi david,
>
> > many thanks for your help there. i initially tried the inheritance
> > method - buut found that my tree traversal broke when trying to
> > traverse a tree made of different types (ie, Node & Jobs). maybe i
> > did something wrong? ie, should i be able to make a tree from those
> > two types if derived from a common model. or is each derived model
> > incompatible with each other?
>
> > cheers,
>
> > paul
>
> > On Oct 7, 11:16 am, David Hall <[EMAIL PROTECTED]> wrote:
> >> Hi Paul,
>
> >> You've got a couple of options for this. The first uses inheritance:
>
> >> class Node(models.Model):
> >> parent = models.ForeignKey("Node", blank=True, null=True,
> >> related_name="children")
>
> >> class Job(Node):
> >> pass
>
> >> class Shot(Node):
> >> pass
>
> >> The second uses generic foreign keys:
>
> >> class Job(models.Model):
> >> parent_type = models.ForeignKey("contenttypes.ContentType")
> >> parent_id = models.PositiveIntegerField(db_index=True)
> >> parent = GenerticForeignKey("parent_type", "parent_id")
>
> >> class Shot(models.Model):
> >> parent_type = models.ForeignKey("contenttypes.ContentType")
> >> parent_id = models.PositiveIntegerField(db_index=True)
> >> parent = GenerticForeignKey("parent_type", "parent_id")
>
> >> Personally, I'd go with the first, as it will integrate better with the
> >> Djano admin application. To traverse the tree, use the Node model.
> >> Once you have got to your required location in the tree, use node.job or
> >> node.shot to get the rest of the information.
>
> >> David.
>
> >> paul wrote:
> >>> hi,
> >>> I'm designing my first django app and would appreciate any advice how
> >>> best to organise my models.
> >>> I have a hierarchal model called Node. this allows me to create a
> >>> hierarchy of nodes - and perform hierarchal operatoins. So far so
> >>> good. each node can be of two 'types':
> >>> 1/ job
> >>> 2/ shot
> >>> I did originally try and make shot & job inherit the Node model.
> >>> However, they couldn't 'link' together (ie, using self as a
> >>> ForeignKey) - as they're of different types. So i've made each of
> >>> these two node types into seperate models. each Node should only be
> >>> linked to one type at a time. From the manual/book - i belive that
> >>> GenericForeignKey is the way to go. ie, insert a GenericForeignKey
> >>> field into the Node. Does this sound like a good approach?
> >>> Many Thanks in Advance,
> >>> Paul
> >> --
> >> David Hall
> >> Technical Lead
> >> Etianen.com
> >> Tel: 07896 106290
>
> >> Email [EMAIL PROTECTED]
> >> Web www.etianen.com
> >> -------------------------------------------------------------------
> >> Ask for help at [EMAIL PROTECTED]
> >> Etianen.com is a small, professional web development agency that
> >> specialises in fast-paced, creative development.
> >> ----------------- enlightened website development -----------------
>
> --
> David Hall
> Technical Lead
> Etianen.com
> Tel: 07896 106290
>
> Email [EMAIL PROTECTED]
> Web www.etianen.com
> -------------------------------------------------------------------
> Ask for help at [EMAIL PROTECTED]
> Etianen.com is a small, professional web development agency that
> specialises in fast-paced, creative development.
> ----------------- enlightened website development -----------------
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