mirror of https://github.com/django/django.git
83 lines
2.3 KiB
Python
83 lines
2.3 KiB
Python
"""
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5. Many-to-many relationships
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To define a many-to-many relationship, use ManyToManyField().
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In this example, an article can be published in multiple publications,
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and a publication has multiple articles.
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"""
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from django.core import meta
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class Publication(meta.Model):
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title = meta.CharField(maxlength=30)
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def __repr__(self):
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return self.title
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class Article(meta.Model):
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headline = meta.CharField(maxlength=100)
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publications = meta.ManyToManyField(Publication)
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def __repr__(self):
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return self.headline
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API_TESTS = """
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# Create a couple of Publications.
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>>> p1 = publications.Publication(id=None, title='The Python Journal')
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>>> p1.save()
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>>> p2 = publications.Publication(id=None, title='Science News')
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>>> p2.save()
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# Create an Article.
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>>> a1 = articles.Article(id=None, headline='Django lets you build Web apps easily')
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>>> a1.save()
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# Associate the Article with one Publication. set_publications() returns a
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# boolean, representing whether any records were added or deleted.
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>>> a1.set_publications([p1.id])
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True
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# If we set it again, it'll return False, because the list of Publications
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# hasn't changed.
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>>> a1.set_publications([p1.id])
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False
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# Create another Article, and set it to appear in both Publications.
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>>> a2 = articles.Article(id=None, headline='NASA uses Python')
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>>> a2.save()
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>>> a2.set_publications([p1.id, p2.id])
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True
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>>> a2.set_publications([p1.id])
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True
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>>> a2.set_publications([p1.id, p2.id])
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True
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# Article objects have access to their related Publication objects.
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>>> a1.get_publication_list()
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[The Python Journal]
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>>> a2.get_publication_list()
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[The Python Journal, Science News]
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# Publication objects have access to their related Article objects.
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>>> p2.get_article_list()
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[NASA uses Python]
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>>> p1.get_article_list(order_by=['headline'])
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[Django lets you build Web apps easily, NASA uses Python]
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# If we delete a Publication, its Articles won't be able to access it.
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>>> p1.delete()
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>>> publications.get_list()
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[Science News]
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>>> a1 = articles.get_object(pk=1)
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>>> a1.get_publication_list()
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[]
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# If we delete an Article, its Publications won't be able to access it.
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>>> a2.delete()
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>>> articles.get_list()
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[Django lets you build Web apps easily]
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>>> p1.get_article_list(order_by=['headline'])
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[Django lets you build Web apps easily]
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"""
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