mirror of https://github.com/django/django.git
49 lines
1.2 KiB
Python
49 lines
1.2 KiB
Python
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"""
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11. Relating an object to itself, many-to-one
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To define a many-to-one relationship between a model and itself, use
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``ForeignKey('self')``.
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In this example, a ``Category`` is related to itself. That is, each
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``Category`` has a parent ``Category``.
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Because of this recursive relationship, we need to tell Django what the
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relationships should be called. Set ``rel_name`` for this, and set
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``related_name`` to designate what the reverse relationship is called.
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"""
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from django.core import meta
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class Category(meta.Model):
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module_name = 'categories'
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fields = (
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meta.CharField('name', maxlength=20),
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meta.ForeignKey('self', null=True,
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rel_name='parent', related_name='child'),
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)
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def __repr__(self):
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return self.name
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API_TESTS = """
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# Create a few Category objects.
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>>> r = categories.Category(id=None, name='Root category', parent_id=None)
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>>> r.save()
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>>> c = categories.Category(id=None, name='Child category', parent_id=r.id)
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>>> c.save()
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>>> r.get_child_list()
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[Child category]
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>>> r.get_child(name__startswith='Child')
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Child category
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>>> r.get_parent()
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Traceback (most recent call last):
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...
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CategoryDoesNotExist
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>>> c.get_child_list()
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[]
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>>> c.get_parent()
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Root category
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"""
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