recursive relationship foreignkey

[Francis Lavoie]

Hi,


I'm trying to implement a recursive relationship with a foreignkey, but I 
failed to make it work.
My goal is to have a table containing different categories and sub categories 
of equipment. the relationship with 'self' is for the subcategories.

But I can't create the Master categories. here's my error:

        Traceback (most recent call last):
        
          File
        "/usr/lib/python2.5/site-packages/django/core/handlers/base.py",
        line 77, in get_response
            response = callback(request, *callback_args,
        **callback_kwargs)
        
          File
        
"/usr/lib/python2.5/site-packages/django/contrib/admin/views/decorators.py", 
line 55, in _checklogin
            return view_func(request, *args, **kwargs)
        
          File
        "/usr/lib/python2.5/site-packages/django/views/decorators/cache.py", 
line 39, in _wrapped_view_func
            response = view_func(request, *args, **kwargs)
        
          File
        "/usr/lib/python2.5/site-packages/django/contrib/admin/views/main.py", 
line 261, in add_stage
            new_object = manipulator.save(new_data)
        
          File
        "/usr/lib/python2.5/site-packages/django/db/models/manipulators.py", 
line 110, in save
            new_object.save()
        
          File
        "/usr/lib/python2.5/site-packages/django/db/models/base.py",
        line 247, in save
            ','.join(placeholders)), db_values)
        
          File "/usr/lib/python2.5/site-packages/MySQLdb/cursors.py",
        line 164, in execute
            self.errorhandler(self, exc, value)
        
          File
        "/usr/lib/python2.5/site-packages/MySQLdb/connections.py", line
        35, in defaulterrorhandler
            raise errorclass, errorvalue
        
        OperationalError: (1048, "Column 'parent_id' cannot be null") 
        
        

here's my object :

        
        class Category(models.Model):
            name = models.CharField(max_length=36)
            description = models.CharField(max_length=200)
            parent = models.ForeignKey('self',blank=True)
        
            class Admin:
                # Admin options go here
                pass


If I dont use blank=True, the admin interface doesn't let me add the category, 
otherwise I received the error.

Any help would be appreciated.

Thank you

Francis


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