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"""
20. Multiple many-to-many relationships between the same two tables
In this example, an Article can have many Categories (as "primary") and many
Categories (as "secondary").
Set ``related_name`` to designate what the reverse relationship is called.
Set ``singular`` to designate what the category object is called. This is
required if a model has multiple ``ManyToManyFields`` to the same object.
"""
from django.core import meta
class Category(meta.Model):
name = meta.CharField(maxlength=20)
class META:
module_name = 'categories'
ordering = ('name',)
def __repr__(self):
return self.name
class Article(meta.Model):
headline = meta.CharField(maxlength=50)
pub_date = meta.DateTimeField()
primary_categories = meta.ManyToManyField(Category,
singular='primary_category', related_name='primary_article')
secondary_categories = meta.ManyToManyField(Category,
singular='secondary_category', related_name='secondary_article')
class META:
ordering = ('pub_date',)
def __repr__(self):
return self.headline
API_TESTS = """
>>> from datetime import datetime
>>> c1 = categories.Category(name='Sports')
>>> c1.save()
>>> c2 = categories.Category(name='News')
>>> c2.save()
>>> c3 = categories.Category(name='Crime')
>>> c3.save()
>>> c4 = categories.Category(name='Life')
>>> c4.save()
>>> a1 = articles.Article(headline='Area man steals', pub_date=datetime(2005, 11, 27))
>>> a1.save()
>>> a1.set_primary_categories([c2.id, c3.id])
True
>>> a1.set_secondary_categories([c4.id])
True
>>> a2 = articles.Article(headline='Area man runs', pub_date=datetime(2005, 11, 28))
>>> a2.save()
>>> a2.set_primary_categories([c1.id, c2.id])
True
>>> a2.set_secondary_categories([c4.id])
True
# The "primary_category" here comes from the "singular" parameter. If we hadn't
# specified the "singular" parameter, Django would just use "category", which
# would cause a conflict because the "primary_categories" and
# "secondary_categories" fields both relate to Category.
>>> a1.get_primary_category_list()
[Crime, News]
# Ditto for the "primary_category" here.
>>> a2.get_primary_category_list()
[News, Sports]
# Ditto for the "secondary_category" here.
>>> a1.get_secondary_category_list()
[Life]
# Ditto for the "secondary_category" here.
>>> a2.get_secondary_category_list()
[Life]
>>> c1.get_primary_article_list()
[Area man runs]
>>> c1.get_secondary_article_list()
[]
>>> c2.get_primary_article_list()
[Area man steals, Area man runs]
>>> c2.get_secondary_article_list()
[]
>>> c3.get_primary_article_list()
[Area man steals]
>>> c3.get_secondary_article_list()
[]
>>> c4.get_primary_article_list()
[]
>>> c4.get_secondary_article_list()
[Area man steals, Area man runs]
"""
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