Found the solution myself:
It seems that you must have both "null=True" and "blank=True" to get
the desired behavior of "not required" for the "Parent" field. My
modified model has this line now:
Parent = models.ForeignKey("self", null=True, blank=True,
verbose_name="ParentFolder")
On Sep 13, 4:32 pm, Martin Taylor <[EMAIL PROTECTED]> wrote:
> I've created a very simple Django app to model a tree (like a file
> system directory tree). Here's the model.py file:
>
> from django.db import models
> #
> # Define constants used to control sizes of DB fields
> #
> MAX_NAME = 100 # Maximum size of an object's Name field
> #
> # Create your models here.
> #
> class Folder(models.Model) :
> """
> This class models the Folder tree.
> """
> #
> # Field definitions
> #
> Parent = models.ForeignKey("self", null=True, verbose_name="Parent
> Folder")
> Name = models.CharField(maxlength=MAX_NAME)
> #
> # Meta options
> #
> class Meta :
> db_table = "Folder"
> #
> # Admin options
> #
> class Admin :
> pass
>
> When I try to add my first Folder in the Admin pages it says:
> "Please correct the error below.
> * This field is required."
> for the Parent field.
>
> Obviously the first folder in the folder tree, or any top level
> folder, will not have a Parent. I don't really want to create an
> artificial top level Parent like "root". Any explanation of why this
> is happening and what to do to fix it would be greatly appreciated.
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