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271 lines
9.5 KiB
271 lines
9.5 KiB
""" |
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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 ``Publication`` |
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objects, and a ``Publication`` has multiple ``Article`` objects. |
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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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# You can't associate it with a Publication until it's been saved. |
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>>> a1.publications.add(p1) |
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Traceback (most recent call last): |
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... |
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ValueError: 'Article' instance needs to have a primary key value before a many-to-many relationship can be used. |
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# Save it! |
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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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