Module Expr Str ImportFrom alias ClassDef bases AttributeLoad NameLoad attr body Assign NameStore Call AttributeLoad NameLoad attr keyword Num FunctionDef arguments args NameParam defaults body Return AttributeLoad NameLoad attr decorator_list ClassDef bases body Assign NameStore TupleLoad Str decorator_list decorator_list ClassDef bases AttributeLoad NameLoad attr body Assign NameStore Call AttributeLoad NameLoad attr keyword Num Assign NameStore Call AttributeLoad NameLoad attr NameLoad FunctionDef arguments args NameParam defaults body Return AttributeLoad NameLoad attr decorator_list ClassDef bases body Assign NameStore TupleLoad Str decorator_list decorator_list Assign NameStore Dict Str Str
N/A N/A 
5. Many-to-many relationships

To define a many-to-many relationship, use ManyToManyField().

In this example, an article can be published in multiple publications,
and a publication has multiple articles.
 django.db models Publication N/A N/A models Model N/A N/A title N/A N/A models CharField maxlength 30 __str__ N/A N/A self N/A N/A N/A N/A self title N/A Meta N/A N/A N/A ordering N/A title N/A N/A Article N/A N/A models Model N/A N/A headline N/A N/A models CharField maxlength 100 N/A publications N/A N/A models ManyToManyField Publication __str__ N/A N/A self N/A N/A N/A N/A self headline N/A Meta N/A N/A N/A ordering N/A headline N/A N/A N/A __test__ N/A API_TESTS 
# Create a couple of Publications.
>>> p1 = Publication(id=None, title='The Python Journal')
>>> p1.save()
>>> p2 = Publication(id=None, title='Science News')
>>> p2.save()
>>> p3 = Publication(id=None, title='Science Weekly')
>>> p3.save()

# Create an Article.
>>> a1 = Article(id=None, headline='Django lets you build Web apps easily')
>>> a1.save()

# Associate the Article with a Publication.
>>> a1.publications.add(p1)

# Create another Article, and set it to appear in both Publications.
>>> a2 = Article(id=None, headline='NASA uses Python')
>>> a2.save()
>>> a2.publications.add(p1, p2)
>>> a2.publications.add(p3)

# Adding a second time is OK
>>> a2.publications.add(p3)

# Add a Publication directly via publications.add by using keyword arguments.
>>> new_publication = a2.publications.create(title='Highlights for Children')

# Article objects have access to their related Publication objects.
>>> a1.publications.all()
[<Publication: The Python Journal>]
>>> a2.publications.all()
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]

# Publication objects have access to their related Article objects.
>>> p2.article_set.all()
[<Article: NASA uses Python>]
>>> p1.article_set.all()
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
>>> Publication.objects.get(id=4).article_set.all()
[<Article: NASA uses Python>]

# We can perform kwarg queries across m2m relationships
>>> Article.objects.filter(publications__id__exact=1)
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
>>> Article.objects.filter(publications__pk=1)
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
>>> Article.objects.filter(publications=1)
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
>>> Article.objects.filter(publications=p1)
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]

>>> Article.objects.filter(publications__title__startswith="Science")
[<Article: NASA uses Python>, <Article: NASA uses Python>]

>>> Article.objects.filter(publications__title__startswith="Science").distinct()
[<Article: NASA uses Python>]

# The count() function respects distinct() as well.
>>> Article.objects.filter(publications__title__startswith="Science").count()
2

>>> Article.objects.filter(publications__title__startswith="Science").distinct().count()
1

>>> Article.objects.filter(publications__in=[1,2]).distinct()
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
>>> Article.objects.filter(publications__in=[1,p2]).distinct()
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
>>> Article.objects.filter(publications__in=[p1,p2]).distinct()
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]

# Reverse m2m queries are supported (i.e., starting at the table that doesn't
# have a ManyToManyField).
>>> Publication.objects.filter(id__exact=1)
[<Publication: The Python Journal>]
>>> Publication.objects.filter(pk=1)
[<Publication: The Python Journal>]

>>> Publication.objects.filter(article__headline__startswith="NASA")
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]

>>> Publication.objects.filter(article__id__exact=1)
[<Publication: The Python Journal>]
>>> Publication.objects.filter(article__pk=1)
[<Publication: The Python Journal>]
>>> Publication.objects.filter(article=1)
[<Publication: The Python Journal>]
>>> Publication.objects.filter(article=a1)
[<Publication: The Python Journal>]

>>> Publication.objects.filter(article__in=[1,2]).distinct()
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
>>> Publication.objects.filter(article__in=[1,a2]).distinct()
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
>>> Publication.objects.filter(article__in=[a1,a2]).distinct()
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]

# If we delete a Publication, its Articles won't be able to access it.
>>> p1.delete()
>>> Publication.objects.all()
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>]
>>> a1 = Article.objects.get(pk=1)
>>> a1.publications.all()
[]

# If we delete an Article, its Publications won't be able to access it.
>>> a2.delete()
>>> Article.objects.all()
[<Article: Django lets you build Web apps easily>]
>>> p2.article_set.all()
[]

# Adding via the 'other' end of an m2m
>>> a4 = Article(headline='NASA finds intelligent life on Earth')
>>> a4.save()
>>> p2.article_set.add(a4)
>>> p2.article_set.all()
[<Article: NASA finds intelligent life on Earth>]
>>> a4.publications.all()
[<Publication: Science News>]

# Adding via the other end using keywords
>>> new_article = p2.article_set.create(headline='Oxygen-free diet works wonders')
>>> p2.article_set.all()
[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
>>> a5 = p2.article_set.all()[1]
>>> a5.publications.all()
[<Publication: Science News>]

# Removing publication from an article:
>>> a4.publications.remove(p2)
>>> p2.article_set.all()
[<Article: Oxygen-free diet works wonders>]
>>> a4.publications.all()
[]

# And from the other end
>>> p2.article_set.remove(a5)
>>> p2.article_set.all()
[]
>>> a5.publications.all()
[]

# Relation sets can be assigned. Assignment clears any existing set members
>>> p2.article_set = [a4, a5]
>>> p2.article_set.all()
[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
>>> a4.publications.all()
[<Publication: Science News>]
>>> a4.publications = [p3]
>>> p2.article_set.all()
[<Article: Oxygen-free diet works wonders>]
>>> a4.publications.all()
[<Publication: Science Weekly>]

# Relation sets can be cleared:
>>> p2.article_set.clear()
>>> p2.article_set.all()
[]
>>> a4.publications.all()
[<Publication: Science Weekly>]

# And you can clear from the other end
>>> p2.article_set.add(a4, a5)
>>> p2.article_set.all()
[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
>>> a4.publications.all()
[<Publication: Science News>, <Publication: Science Weekly>]
>>> a4.publications.clear()
>>> a4.publications.all()
[]
>>> p2.article_set.all()
[<Article: Oxygen-free diet works wonders>]

# Relation sets can also be set using primary key values
>>> p2.article_set = [a4.id, a5.id]
>>> p2.article_set.all()
[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]
>>> a4.publications.all()
[<Publication: Science News>]
>>> a4.publications = [p3.id]
>>> p2.article_set.all()
[<Article: Oxygen-free diet works wonders>]
>>> a4.publications.all()
[<Publication: Science Weekly>]

# Recreate the article and Publication we have deleted.
>>> p1 = Publication(id=None, title='The Python Journal')
>>> p1.save()
>>> a2 = Article(id=None, headline='NASA uses Python')
>>> a2.save()
>>> a2.publications.add(p1, p2, p3)

# Bulk delete some Publications - references to deleted publications should go
>>> Publication.objects.filter(title__startswith='Science').delete()
>>> Publication.objects.all()
[<Publication: Highlights for Children>, <Publication: The Python Journal>]
>>> Article.objects.all()
[<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>]
>>> a2.publications.all()
[<Publication: The Python Journal>]

# Bulk delete some articles - references to deleted objects should go
>>> q = Article.objects.filter(headline__startswith='Django')
>>> print q
[<Article: Django lets you build Web apps easily>]
>>> q.delete()

# After the delete, the QuerySet cache needs to be cleared, and the referenced objects should be gone
>>> print q
[]
>>> p1.article_set.all()
[<Article: NASA uses Python>]

# An alternate to calling clear() is to assign the empty set
>>> p1.article_set = []
>>> p1.article_set.all()
[]

>>> a2.publications = [p1, new_publication]
>>> a2.publications.all()
[<Publication: Highlights for Children>, <Publication: The Python Journal>]
>>> a2.publications = []
>>> a2.publications.all()
[]

