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Code Issues Releases Wiki Activity

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
API facilities.
Create a couple of Publications::
Create a couple of ``Publications``::
>>> p1 = Publication(title='The Python Journal')
>>> p1.save()
@ -44,11 +44,11 @@ Create a couple of Publications::
>>> p3 = Publication(title='Science Weekly')
>>> p3.save()
Create an Article::
Create an ``Article``::
>>> 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)
Traceback (most recent call last):
@ -60,11 +60,11 @@ Save it!
>>> a1.save()
Associate the Article with a Publication::
Associate the ``Article`` with a ``Publication``::
>>> 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.save()
@ -75,25 +75,26 @@ Adding a second time is OK::
>>> 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)
Traceback (most recent call last):
...
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')
Article objects have access to their related Publication objects::
``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::
``Publication`` objects have access to their related ``Article`` objects::
>>> p2.article_set.all()
[<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()
[<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: 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: 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()
2
@ -133,7 +136,7 @@ The count() function respects distinct() as well::
[<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)::
a :class:`~django.db.models.ManyToManyField`)::
>>> Publication.objects.filter(id__exact=1)
[<Publication: The Python Journal>]
@ -163,7 +166,7 @@ involved is a little complex)::
>>> Article.objects.exclude(publications=p2)
[<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()
>>> Publication.objects.all()
@ -172,7 +175,7 @@ If we delete a Publication, its Articles won't be able to access it::
>>> 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()
>>> Article.objects.all()
@ -199,7 +202,7 @@ Adding via the other end using keywords::
>>> a5.publications.all()
[<Publication: Science News>]
Removing publication from an article::
Removing ``Publication`` from an ``Article``::
>>> a4.publications.remove(p2)
>>> p2.article_set.all()
@ -242,7 +245,7 @@ And you can clear from the other end::
>>> p2.article_set.all()
[<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.save()
@ -250,7 +253,8 @@ Recreate the article and Publication we have deleted::
>>> a2.save()
>>> 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.all()
@ -267,15 +271,18 @@ Bulk delete some articles - references to deleted objects should go::
[<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::
After the :meth:`~django.db.models.query.QuerySet.delete`, the
:class:`~django.db.models.query.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::
An alternate to calling
:meth:`~django.db.models.fields.related.RelatedManager.clear` is to assign the
empty set::
>>> p1.article_set = []
>>> p1.article_set.all()