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"""
11. Relating an object to itself, many-to-one
To define a many-to-one relationship between a model and itself, use
``ForeignKey('self')``.
In this example, a ``Category`` is related to itself. That is, each
``Category`` has a parent ``Category``.
Set ``related_name`` to designate what the reverse relationship is called.
"""
from django.db import models
class Category(models.Model):
name = models.CharField(max_length=20)
parent = models.ForeignKey('self', blank=True, null=True, related_name='child_set')
def __unicode__(self):
return self.name
__test__ = {'API_TESTS':"""
# Create a few Category objects.
>>> r = Category(id=None, name='Root category', parent=None)
>>> r.save()
>>> c = Category(id=None, name='Child category', parent=r)
>>> c.save()
>>> r.child_set.all()
[<Category: Child category>]
>>> r.child_set.get(name__startswith='Child')
<Category: Child category>
>>> print r.parent
None
>>> c.child_set.all()
[]
>>> c.parent
<Category: Root category>
"""}
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