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33a0862215
This means we can now do nested SQL queries (since we need nested queries to get the right answer). It requires poking directly at the Query class. Might add support for this through QuerySets later. git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@7170 bcc190cf-cafb-0310-a4f2-bffc1f526a37
264 lines
9.2 KiB
Python
264 lines
9.2 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(max_length=30)
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def __unicode__(self):
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return self.title
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class Meta:
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ordering = ('title',)
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class Article(models.Model):
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headline = models.CharField(max_length=100)
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publications = models.ManyToManyField(Publication)
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def __unicode__(self):
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return self.headline
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class Meta:
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ordering = ('headline',)
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__test__ = {'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 a Publication.
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>>> a1.publications.add(p1)
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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.publications.add(p1, p2)
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>>> a2.publications.add(p3)
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# Adding a second time is OK
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>>> a2.publications.add(p3)
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# Add a Publication directly via publications.add by using keyword arguments.
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>>> new_publication = a2.publications.create(title='Highlights for Children')
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# Article objects have access to their related Publication objects.
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>>> a1.publications.all()
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[<Publication: The Python Journal>]
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>>> a2.publications.all()
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[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
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# Publication objects have access to their related Article objects.
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>>> p2.article_set.all()
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[<Article: NASA uses Python>]
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>>> p1.article_set.all()
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Publication.objects.get(id=4).article_set.all()
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[<Article: NASA uses Python>]
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# We can perform kwarg queries across m2m relationships
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>>> Article.objects.filter(publications__id__exact=1)
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications__pk=1)
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications=1)
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications=p1)
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications__title__startswith="Science")
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[<Article: NASA uses Python>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications__title__startswith="Science").distinct()
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[<Article: NASA uses Python>]
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# The count() function respects distinct() as well.
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>>> Article.objects.filter(publications__title__startswith="Science").count()
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2
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>>> Article.objects.filter(publications__title__startswith="Science").distinct().count()
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1
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>>> Article.objects.filter(publications__in=[1,2]).distinct()
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications__in=[1,p2]).distinct()
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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>>> Article.objects.filter(publications__in=[p1,p2]).distinct()
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[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
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# Reverse m2m queries are supported (i.e., starting at the table that doesn't
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# have a ManyToManyField).
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>>> Publication.objects.filter(id__exact=1)
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[<Publication: The Python Journal>]
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>>> Publication.objects.filter(pk=1)
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[<Publication: The Python Journal>]
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>>> Publication.objects.filter(article__headline__startswith="NASA")
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[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
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>>> Publication.objects.filter(article__id__exact=1)
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[<Publication: The Python Journal>]
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>>> Publication.objects.filter(article__pk=1)
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[<Publication: The Python Journal>]
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>>> Publication.objects.filter(article=1)
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[<Publication: The Python Journal>]
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>>> Publication.objects.filter(article=a1)
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[<Publication: The Python Journal>]
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>>> Publication.objects.filter(article__in=[1,2]).distinct()
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[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
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>>> Publication.objects.filter(article__in=[1,a2]).distinct()
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[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
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>>> Publication.objects.filter(article__in=[a1,a2]).distinct()
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[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
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# Excluding a related item works as you would expect, too (although the SQL
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# involved is a little complex).
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>>> Article.objects.exclude(publications=p2)
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[<Article: Django lets you build Web apps easily>]
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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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>>> Publication.objects.all()
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[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>]
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>>> a1 = Article.objects.get(pk=1)
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>>> a1.publications.all()
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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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>>> Article.objects.all()
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[<Article: Django lets you build Web apps easily>]
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>>> p2.article_set.all()
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[]
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# Adding via the 'other' end of an m2m
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>>> a4 = Article(headline='NASA finds intelligent life on Earth')
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>>> a4.save()
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>>> p2.article_set.add(a4)
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>>> p2.article_set.all()
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[<Article: NASA finds intelligent life on Earth>]
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>>> a4.publications.all()
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[<Publication: Science News>]
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# Adding via the other end using keywords
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>>> new_article = p2.article_set.create(headline='Oxygen-free diet works wonders')
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>>> p2.article_set.all()
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[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
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>>> a5 = p2.article_set.all()[1]
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>>> a5.publications.all()
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[<Publication: Science News>]
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# Removing publication from an article:
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>>> a4.publications.remove(p2)
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>>> p2.article_set.all()
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[<Article: Oxygen-free diet works wonders>]
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>>> a4.publications.all()
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[]
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# And from the other end
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>>> p2.article_set.remove(a5)
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>>> p2.article_set.all()
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[]
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>>> a5.publications.all()
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[]
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# Relation sets can be assigned. Assignment clears any existing set members
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>>> p2.article_set = [a4, a5]
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>>> p2.article_set.all()
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[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
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>>> a4.publications.all()
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[<Publication: Science News>]
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>>> a4.publications = [p3]
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>>> p2.article_set.all()
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[<Article: Oxygen-free diet works wonders>]
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>>> a4.publications.all()
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[<Publication: Science Weekly>]
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# Relation sets can be cleared:
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>>> p2.article_set.clear()
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>>> p2.article_set.all()
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[]
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>>> a4.publications.all()
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[<Publication: Science Weekly>]
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# And you can clear from the other end
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>>> p2.article_set.add(a4, a5)
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>>> p2.article_set.all()
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[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
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>>> a4.publications.all()
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[<Publication: Science News>, <Publication: Science Weekly>]
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>>> a4.publications.clear()
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>>> a4.publications.all()
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[]
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>>> p2.article_set.all()
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[<Article: Oxygen-free diet works wonders>]
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# Relation sets can also be set using primary key values
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>>> p2.article_set = [a4.id, a5.id]
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>>> p2.article_set.all()
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[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
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>>> a4.publications.all()
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[<Publication: Science News>]
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>>> a4.publications = [p3.id]
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>>> p2.article_set.all()
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[<Article: Oxygen-free diet works wonders>]
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>>> a4.publications.all()
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[<Publication: Science Weekly>]
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# Recreate the article and Publication we have deleted.
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>>> p1 = Publication(id=None, title='The Python Journal')
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>>> p1.save()
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>>> a2 = Article(id=None, headline='NASA uses Python')
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>>> a2.save()
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>>> a2.publications.add(p1, p2, p3)
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# Bulk delete some Publications - references to deleted publications should go
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>>> Publication.objects.filter(title__startswith='Science').delete()
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>>> Publication.objects.all()
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[<Publication: Highlights for Children>, <Publication: The Python Journal>]
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>>> Article.objects.all()
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[<Article: Django lets you build Web apps easily>, <Article: NASA finds intelligent life on Earth>, <Article: NASA uses Python>, <Article: Oxygen-free diet works wonders>]
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>>> a2.publications.all()
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[<Publication: The Python Journal>]
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# Bulk delete some articles - references to deleted objects should go
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>>> q = Article.objects.filter(headline__startswith='Django')
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>>> print q
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[<Article: Django lets you build Web apps easily>]
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>>> q.delete()
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# After the delete, the QuerySet cache needs to be cleared, and the referenced objects should be gone
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>>> print q
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[]
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>>> p1.article_set.all()
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[<Article: NASA uses Python>]
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# An alternate to calling clear() is to assign the empty set
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>>> p1.article_set = []
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>>> p1.article_set.all()
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[]
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>>> a2.publications = [p1, new_publication]
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>>> a2.publications.all()
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[<Publication: Highlights for Children>, <Publication: The Python Journal>]
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>>> a2.publications = []
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>>> a2.publications.all()
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[]
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"""}
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