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Fixed #19756 - Corrected a ManyToMany example and added some links and markup.

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Tim Graham 2013-02-07 06:12:25 -05:00
parent 720888a146
commit 43efefae69
1 changed files with 27 additions and 20 deletions
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47
docs/topics/db/examples/many_to_many.txt
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@ -35,7 +35,7 @@ objects, and a ``Publication`` has multiple ``Article`` objects:
What follows are examples of operations that can be performed using the Python What follows are examples of operations that can be performed using the Python
API facilities. API facilities.
Create a couple of Publications:: Create a couple of ``Publications``::
>>> p1 = Publication(title='The Python Journal') >>> p1 = Publication(title='The Python Journal')
>>> p1.save() >>> p1.save()
@ -44,11 +44,11 @@ Create a couple of Publications::
>>> p3 = Publication(title='Science Weekly') >>> p3 = Publication(title='Science Weekly')
>>> p3.save() >>> p3.save()
Create an Article:: Create an ``Article``::
>>> a1 = Article(headline='Django lets you build Web apps easily') >>> a1 = Article(headline='Django lets you build Web apps easily')
You can't associate it with a Publication until it's been saved:: You can't associate it with a ``Publication`` until it's been saved::
>>> a1.publications.add(p1) >>> a1.publications.add(p1)
Traceback (most recent call last): Traceback (most recent call last):
@ -60,11 +60,11 @@ Save it!
>>> a1.save() >>> a1.save()
Associate the Article with a Publication:: Associate the ``Article`` with a ``Publication``::
>>> a1.publications.add(p1) >>> a1.publications.add(p1)
Create another Article, and set it to appear in both Publications:: Create another ``Article``, and set it to appear in both ``Publications``::
>>> a2 = Article(headline='NASA uses Python') >>> a2 = Article(headline='NASA uses Python')
>>> a2.save() >>> a2.save()
@ -75,25 +75,26 @@ Adding a second time is OK::
>>> a2.publications.add(p3) >>> a2.publications.add(p3)
Adding an object of the wrong type raises TypeError:: Adding an object of the wrong type raises :exc:`~exceptions.TypeError`::
>>> a2.publications.add(a1) >>> a2.publications.add(a1)
Traceback (most recent call last): Traceback (most recent call last):
... ...
TypeError: 'Publication' instance expected TypeError: 'Publication' instance expected
Add a Publication directly via publications.add by using keyword arguments:: Create and add a ``Publication`` to an ``Article`` in one step using
:meth:`~django.db.models.fields.related.RelatedManager.create`::
>>> new_publication = a2.publications.create(title='Highlights for Children') >>> new_publication = a2.publications.create(title='Highlights for Children')
Article objects have access to their related Publication objects:: ``Article`` objects have access to their related ``Publication`` objects::
>>> a1.publications.all() >>> a1.publications.all()
[<Publication: The Python Journal>] [<Publication: The Python Journal>]
>>> a2.publications.all() >>> a2.publications.all()
[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>] [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]
Publication objects have access to their related Article objects:: ``Publication`` objects have access to their related ``Article`` objects::
>>> p2.article_set.all() >>> p2.article_set.all()
[<Article: NASA uses Python>] [<Article: NASA uses Python>]
@ -102,7 +103,8 @@ Publication objects have access to their related Article objects::
>>> Publication.objects.get(id=4).article_set.all() >>> Publication.objects.get(id=4).article_set.all()
[<Article: NASA uses Python>] [<Article: NASA uses Python>]
Many-to-many relationships can be queried using :ref:`lookups across relationships <lookups-that-span-relationships>`:: Many-to-many relationships can be queried using :ref:`lookups across
relationships <lookups-that-span-relationships>`::
>>> Article.objects.filter(publications__id__exact=1) >>> Article.objects.filter(publications__id__exact=1)
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>] [<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]
@ -119,7 +121,8 @@ Many-to-many relationships can be queried using :ref:`lookups across relationshi
>>> Article.objects.filter(publications__title__startswith="Science").distinct() >>> Article.objects.filter(publications__title__startswith="Science").distinct()
[<Article: NASA uses Python>] [<Article: NASA uses Python>]
The count() function respects distinct() as well:: The :meth:`~django.db.models.query.QuerySet.count` function respects
:meth:`~django.db.models.query.QuerySet.distinct` as well::
>>> Article.objects.filter(publications__title__startswith="Science").count() >>> Article.objects.filter(publications__title__startswith="Science").count()
2 2
@ -133,7 +136,7 @@ The count() function respects distinct() as well::
[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>] [<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 Reverse m2m queries are supported (i.e., starting at the table that doesn't have
a ManyToManyField):: a :class:`~django.db.models.ManyToManyField`)::
>>> Publication.objects.filter(id__exact=1) >>> Publication.objects.filter(id__exact=1)
[<Publication: The Python Journal>] [<Publication: The Python Journal>]
@ -163,7 +166,7 @@ involved is a little complex)::
>>> Article.objects.exclude(publications=p2) >>> Article.objects.exclude(publications=p2)
[<Article: Django lets you build Web apps easily>] [<Article: Django lets you build Web apps easily>]
If we delete a Publication, its Articles won't be able to access it:: If we delete a ``Publication``, its ``Articles`` won't be able to access it::
>>> p1.delete() >>> p1.delete()
>>> Publication.objects.all() >>> Publication.objects.all()
@ -172,7 +175,7 @@ If we delete a Publication, its Articles won't be able to access it::
>>> a1.publications.all() >>> a1.publications.all()
[] []
If we delete an Article, its Publications won't be able to access it:: If we delete an ``Article``, its ``Publications`` won't be able to access it::
>>> a2.delete() >>> a2.delete()
>>> Article.objects.all() >>> Article.objects.all()
@ -199,7 +202,7 @@ Adding via the other end using keywords::
>>> a5.publications.all() >>> a5.publications.all()
[<Publication: Science News>] [<Publication: Science News>]
Removing publication from an article:: Removing ``Publication`` from an ``Article``::
>>> a4.publications.remove(p2) >>> a4.publications.remove(p2)
>>> p2.article_set.all() >>> p2.article_set.all()
@ -242,7 +245,7 @@ And you can clear from the other end::
>>> p2.article_set.all() >>> p2.article_set.all()
[<Article: Oxygen-free diet works wonders>] [<Article: Oxygen-free diet works wonders>]
Recreate the article and Publication we have deleted:: Recreate the ``Article`` and ``Publication`` we have deleted::
>>> p1 = Publication(title='The Python Journal') >>> p1 = Publication(title='The Python Journal')
>>> p1.save() >>> p1.save()
@ -250,7 +253,8 @@ Recreate the article and Publication we have deleted::
>>> a2.save() >>> a2.save()
>>> a2.publications.add(p1, p2, p3) >>> a2.publications.add(p1, p2, p3)
Bulk delete some Publications - references to deleted publications should go:: Bulk delete some ``Publications`` - references to deleted publications should
go::
>>> Publication.objects.filter(title__startswith='Science').delete() >>> Publication.objects.filter(title__startswith='Science').delete()
>>> Publication.objects.all() >>> Publication.objects.all()
@ -267,15 +271,18 @@ Bulk delete some articles - references to deleted objects should go::
[<Article: Django lets you build Web apps easily>] [<Article: Django lets you build Web apps easily>]
>>> q.delete() >>> q.delete()
After the delete, the QuerySet cache needs to be cleared, and the referenced After the :meth:`~django.db.models.query.QuerySet.delete`, the
objects should be gone:: :class:`~django.db.models.query.QuerySet` cache needs to be cleared, and the
referenced objects should be gone::
>>> print(q) >>> print(q)
[] []
>>> p1.article_set.all() >>> p1.article_set.all()
[<Article: NASA uses Python>] [<Article: NASA uses Python>]
An alternate to calling clear() is to assign the empty set:: An alternate to calling
:meth:`~django.db.models.fields.related.RelatedManager.clear` is to assign the
empty set::
>>> p1.article_set = [] >>> p1.article_set = []
>>> p1.article_set.all() >>> p1.article_set.all()