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
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