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