On Mon, Jul 14, 2008 at 6:27 AM, MarC <[EMAIL PROTECTED]> wrote:
>
> Hello everybody,
>
> I'm trying to come up with the most django simple friendly way to store
> records in a "tree" kind of database. For instance my records are
...
> # Create your models here.
> class Food(models.Model):
> name = models.CharField(max_length=50);
> parents = models.ForeignKey('Food');
> class Admin:
> pass
> >>
>
> But I'm having trouble to create a root "Food" node with no ForeignKey
> defined or ForeignKey pointed to himself from the admin site.
Firstly, if you want to take this apprach, you identify a root node by
setting parents=None. In order to do this, you need to modify your
model to allow the parents field to accept null values (i.e.,
null=True as a setting on the field).
Secondly, while this approach is the easiest way to represent a tree,
it isn't the easiest structure to query. You need to read up on MPTT
(Modified Preorder Tree Traversal). The django-mptt project [1] is
probably also worth looking into - if only because it has some great
links on representing trees in relation databases.
[1] http://code.google.com/p/django-mptt/
Yours,
Russ Magee %-)
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