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git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2157 bcc190cf-cafb-0310-a4f2-bffc1f526a37
112 lines
3.3 KiB
Python
112 lines
3.3 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.db import models
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class Publication(models.Model):
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title = models.CharField(maxlength=30)
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def __repr__(self):
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return self.title
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class Article(models.Model):
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headline = models.CharField(maxlength=100)
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publications = models.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 = Publication(id=None, title='The Python Journal')
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>>> p1.save()
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>>> p2 = Publication(id=None, title='Science News')
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>>> p2.save()
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>>> p3 = Publication(id=None, title='Science Weekly')
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>>> p3.save()
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# Create an Article.
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>>> a1 = 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 = 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, p3.id])
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True
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# Article objects have access to their related Publication objects.
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>>> list(a1.publication_set)
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[The Python Journal]
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>>> list(a2.publication_set)
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[The Python Journal, Science News, Science Weekly]
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# Publication objects have access to their related Article objects.
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>>> list(p2.article_set)
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[NASA uses Python]
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>>> list(p1.article_set.order_by('headline'))
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[Django lets you build Web apps easily, NASA uses Python]
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# We can perform kwarg queries across m2m relationships
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>>> list(Article.objects.filter(publications__id__exact=1))
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[Django lets you build Web apps easily, NASA uses Python]
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>>> list(Article.objects.filter(publications__pk=1))
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[Django lets you build Web apps easily, NASA uses Python]
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>>> list(Article.objects.filter(publications__title__startswith="Science"))
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[NASA uses Python, NASA uses Python]
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>>> list(Article.objects.filter(publications__title__startswith="Science", distinct=True))
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[NASA uses Python]
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# Reverse m2m queries (i.e., start at the table that doesn't have a ManyToManyField)
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>>> list(Publication.objects.filter(id__exact=1))
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[The Python Journal]
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>>> list(Publication.objects.filter(pk=1))
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[The Python Journal]
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>>> list(Publication.objects.filter(article__headline__startswith="NASA"))
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[The Python Journal, Science News, Science Weekly]
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>>> list(Publication.objects.filter(article__id__exact=1))
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[The Python Journal]
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>>> list(Publication.objects.filter(article__pk=1))
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[The Python Journal]
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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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>>> list(Publication.objects)
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[Science News, Science Weekly]
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>>> a1 = Article.objects.get(pk=1)
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>>> list(a1.publication_set)
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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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>>> list(Article.objects)
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[Django lets you build Web apps easily]
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>>> list(p1.article_set.order_by=('headline'))
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[Django lets you build Web apps easily]
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"""
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