documented RelatedManager calling save() behind the scenes, added section on direct replacement of related object set
This commit is contained in:
Matthew Rich
parent
a91799a30c
commit
a5bcc09c8f
|
|
@ -36,89 +36,117 @@ Related objects reference
|
|||
In this example, the methods below will be available both on
|
||||
``topping.pizza_set`` and on ``pizza.toppings``.
|
||||
|
||||
These related managers have some extra methods:
|
||||
.. _related-manager-methods:
|
||||
|
||||
.. method:: add(obj1, [obj2, ...])
|
||||
Related Manager Methods
|
||||
-----------------------
|
||||
|
||||
Adds the specified model objects to the related object set.
|
||||
.. method:: add(obj1, [obj2, ...])
|
||||
|
||||
Example::
|
||||
Adds the specified model objects to the related object set.
|
||||
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = Entry.objects.get(id=234)
|
||||
>>> b.entry_set.add(e) # Associates Entry e with Blog b.
|
||||
Example::
|
||||
|
||||
In the example above, ``e.save()`` is called to perform the update.
|
||||
Using ``add()`` with a many-to-many relationship, however, will not
|
||||
call any ``save()`` methods, but rather create the relationships
|
||||
using :meth:`QuerySet.bulk_create()
|
||||
<django.db.models.query.QuerySet.bulk_create>`. If you need to execute
|
||||
some custom logic when a relationship is created, listen to the
|
||||
:data:`~django.db.models.signals.m2m_changed` signal.
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = Entry.objects.get(id=234)
|
||||
>>> b.entry_set.add(e) # Associates Entry e with Blog b.
|
||||
|
||||
.. method:: create(**kwargs)
|
||||
In the example above, in the case of a
|
||||
:class:`~django.db.models.ForeignKey` relationship,
|
||||
``e.save()`` is called by the related manager to perform the update.
|
||||
Using ``add()`` with a many-to-many relationship, however, will not
|
||||
call any ``save()`` methods, but rather create the relationships
|
||||
using :meth:`QuerySet.bulk_create()
|
||||
<django.db.models.query.QuerySet.bulk_create>`. If you need to execute
|
||||
some custom logic when a relationship is created, listen to the
|
||||
:data:`~django.db.models.signals.m2m_changed` signal.
|
||||
|
||||
Creates a new object, saves it and puts it in the related object set.
|
||||
Returns the newly created object::
|
||||
.. method:: create(**kwargs)
|
||||
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = b.entry_set.create(
|
||||
... headline='Hello',
|
||||
... body_text='Hi',
|
||||
... pub_date=datetime.date(2005, 1, 1)
|
||||
... )
|
||||
Creates a new object, saves it and puts it in the related object set.
|
||||
Returns the newly created object::
|
||||
|
||||
# No need to call e.save() at this point -- it's already been saved.
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = b.entry_set.create(
|
||||
... headline='Hello',
|
||||
... body_text='Hi',
|
||||
... pub_date=datetime.date(2005, 1, 1)
|
||||
... )
|
||||
|
||||
This is equivalent to (but much simpler than)::
|
||||
# No need to call e.save() at this point -- it's already been saved.
|
||||
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = Entry(
|
||||
... blog=b,
|
||||
... headline='Hello',
|
||||
... body_text='Hi',
|
||||
... pub_date=datetime.date(2005, 1, 1)
|
||||
... )
|
||||
>>> e.save(force_insert=True)
|
||||
This is equivalent to (but much simpler than)::
|
||||
|
||||
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``.
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = Entry(
|
||||
... blog=b,
|
||||
... headline='Hello',
|
||||
... body_text='Hi',
|
||||
... pub_date=datetime.date(2005, 1, 1)
|
||||
... )
|
||||
>>> e.save(force_insert=True)
|
||||
|
||||
.. method:: remove(obj1, [obj2, ...])
|
||||
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``.
|
||||
|
||||
Removes the specified model objects from the related object set::
|
||||
.. method:: remove(obj1, [obj2, ...])
|
||||
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = Entry.objects.get(id=234)
|
||||
>>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.
|
||||
Removes the specified model objects from the related object set::
|
||||
|
||||
Similar to :meth:`add()`, ``e.save()`` is called in the example above
|
||||
to perform the update. Using ``remove()`` with a many-to-many
|
||||
relationship, however, will delete the relationships using
|
||||
:meth:`QuerySet.delete()<django.db.models.query.QuerySet.delete>` which
|
||||
means no model ``save()`` methods are called; listen to the
|
||||
:data:`~django.db.models.signals.m2m_changed` signal if you wish to
|
||||
execute custom code when a relationship is deleted.
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> e = Entry.objects.get(id=234)
|
||||
>>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.
|
||||
|
||||
For :class:`~django.db.models.ForeignKey` objects, this method only
|
||||
exists if ``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`` :class:`~django.db.models.ForeignKey` doesn't have
|
||||
``null=True``, this is invalid.
|
||||
Similar to :meth:`add()`, ``e.save()`` is called in the example above
|
||||
to perform the update. Using ``remove()`` with a many-to-many
|
||||
relationship, however, will delete the relationships using
|
||||
:meth:`QuerySet.delete()<django.db.models.query.QuerySet.delete>` which
|
||||
means no model ``save()`` methods are called; listen to the
|
||||
:data:`~django.db.models.signals.m2m_changed` signal if you wish to
|
||||
execute custom code when a relationship is deleted.
|
||||
|
||||
.. method:: clear()
|
||||
For :class:`~django.db.models.ForeignKey` objects, this method only
|
||||
exists if ``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`` :class:`~django.db.models.ForeignKey` doesn't have
|
||||
``null=True``, this is invalid.
|
||||
|
||||
Removes all objects from the related object set::
|
||||
.. method:: clear()
|
||||
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> b.entry_set.clear()
|
||||
Removes all objects from the related object set::
|
||||
|
||||
Note this doesn't delete the related objects -- it just disassociates
|
||||
them.
|
||||
>>> b = Blog.objects.get(id=1)
|
||||
>>> b.entry_set.clear()
|
||||
|
||||
Just like ``remove()``, ``clear()`` is only available on
|
||||
:class:`~django.db.models.ForeignKey`\s where ``null=True``.
|
||||
Note this doesn't delete the related objects -- it just disassociates
|
||||
them.
|
||||
|
||||
Just like ``remove()``, ``clear()`` is only available on
|
||||
:class:`~django.db.models.ForeignKey`\s where ``null=True``.
|
||||
|
||||
.. note::
|
||||
|
||||
Note that ``add()``, ``create()``, ``remove()``, and ``clear()`` all
|
||||
apply database changes immediately for all types of related fields. In other
|
||||
words, there is no need to call ``save()`` on either end of the
|
||||
relationship.
|
||||
|
||||
.. _direct-assignment:
|
||||
|
||||
Direct Assignment
|
||||
-----------------
|
||||
|
||||
A related object set can be replaced in bulk with one operation by assigning a
|
||||
new iterable of objects to it::
|
||||
|
||||
>>> new_list = [obj1, obj2, obj3]
|
||||
>>> e.related_set = new_list
|
||||
|
||||
If the foreign key relationship has ``null=True``, then the related manager
|
||||
will first call ``clear()`` to disassociate any existing objects in the related
|
||||
set before adding the contents of ``new_list``. Otherwise the objects in
|
||||
``new_list`` will be added to the existing related object set.
|
||||
|
|
|
|||
Loading…
Reference in New Issue