mirror of
https://github.com/django/django.git
synced 2024-11-18 15:34:16 +00:00
78 lines
2.6 KiB
Plaintext
78 lines
2.6 KiB
Plaintext
|
.. _ref-models-relations:
|
||
|
|
|
||
|
|
=========================
|
||
|
|
Related objects reference
|
||
|
|
=========================
|
||
|
|
|
||
|
|
Extra methods on managers when used in a ForeignKey context
|
||
|
|
===========================================================
|
||
|
|
|
||
|
|
.. currentmodule:: django.db.models
|
||
|
|
|
||
|
|
.. method:: QuerySet.add(obj1, [obj2, ...])
|
||
|
|
|
||
|
|
Adds the specified model objects to the related object set.
|
||
|
|
|
||
|
|
Example::
|
||
|
|
|
||
|
|
>>> b = Blog.objects.get(id=1)
|
||
|
|
>>> e = Entry.objects.get(id=234)
|
||
|
|
>>> b.entry_set.add(e) # Associates Entry e with Blog b.
|
||
|
|
|
||
|
|
.. method:: QuerySet.create(**kwargs)`
|
||
|
|
|
||
|
|
Creates a new object, saves it and puts it in the related object set.
|
||
|
|
Returns the newly created object::
|
||
|
|
|
||
|
|
>>> b = Blog.objects.get(id=1)
|
||
|
|
>>> e = b.entry_set.create(
|
||
|
|
... headline='Hello',
|
||
|
|
... body_text='Hi',
|
||
|
|
... pub_date=datetime.date(2005, 1, 1)
|
||
|
|
... )
|
||
|
|
|
||
|
|
# No need to call e.save() at this point -- it's already been saved.
|
||
|
|
|
||
|
|
This is equivalent to (but much simpler than)::
|
||
|
|
|
||
|
|
>>> b = Blog.objects.get(id=1)
|
||
|
|
>>> e = Entry(
|
||
|
|
.... blog=b,
|
||
|
|
.... headline='Hello',
|
||
|
|
.... body_text='Hi',
|
||
|
|
.... pub_date=datetime.date(2005, 1, 1)
|
||
|
|
.... )
|
||
|
|
>>> e.save()
|
||
|
|
|
||
|
|
Note that there's no need to specify the keyword argument of the model that
|
||
|
|
defines the relationship. In the above example, we don't pass the parameter
|
||
|
|
``blog`` to ``create()``. Django figures out that the new ``Entry`` object's
|
||
|
|
``blog`` field should be set to ``b``.
|
||
|
|
|
||
|
|
.. method:: QuerySet.remove(obj1, [obj2, ...])
|
||
|
|
|
||
|
|
Removes the specified model objects from the related object set::
|
||
|
|
|
||
|
|
>>> b = Blog.objects.get(id=1)
|
||
|
|
>>> e = Entry.objects.get(id=234)
|
||
|
|
>>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.
|
||
|
|
|
||
|
|
In order to prevent database inconsistency, this method only exists on
|
||
|
|
``ForeignKey`` objects where ``null=True``. If the related field can't be
|
||
|
|
set to ``None`` (``NULL``), then an object can't be removed from a relation
|
||
|
|
without being added to another. In the above example, removing ``e`` from
|
||
|
|
``b.entry_set()`` is equivalent to doing ``e.blog = None``, and because the
|
||
|
|
``blog`` ``ForeignKey`` doesn't have ``null=True``, this is invalid.
|
||
|
|
|
||
|
|
.. method:: QuerySet.clear()
|
||
|
|
|
||
|
|
Removes all objects from the related object set::
|
||
|
|
|
||
|
|
>>> b = Blog.objects.get(id=1)
|
||
|
|
>>> b.entry_set.clear()
|
||
|
|
|
||
|
|
Note this doesn't delete the related objects -- it just disassociates them.
|
||
|
|
|
||
|
|
Just like ``remove()``, ``clear()`` is only available on ``ForeignKey``s
|
||
|
|
where ``null=True``.
|