1 """

     2 11. Relating an object to itself, many-to-one

     3 

     4 To define a many-to-one relationship between a model and itself, use

     5 ``ForeignKey('self')``.

     6 

     7 In this example, a ``Category`` is related to itself. That is, each

     8 ``Category`` has a parent ``Category``.

     9 

    10 Set ``related_name`` to designate what the reverse relationship is called.

    11 """

    12 

    13 from django.db import models

    14 

    15 class Category(models.Model):

    16     name = models.CharField(maxlength=20)

    17     parent = models.ForeignKey('self', null=True, related_name='child_set')

    18 

    19     def __str__(self):

    20         return self.name

    21 

    22 __test__ = {'API_TESTS':"""

    23 # Create a few Category objects.

    24 >>> r = Category(id=None, name='Root category', parent=None)

    25 >>> r.save()

    26 >>> c = Category(id=None, name='Child category', parent=r)

    27 >>> c.save()

    28 

    29 >>> r.child_set.all()

    30 [<Category: Child category>]

    31 >>> r.child_set.get(name__startswith='Child')

    32 <Category: Child category>

    33 >>> print r.parent

    34 None

    35 

    36 >>> c.child_set.all()

    37 []

    38 >>> c.parent

    39 <Category: Root category>

    40 """}