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git-svn-id: http://code.djangoproject.com/svn/django/trunk@4281 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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@ -121,37 +121,19 @@ objects, when you're confident you won't have primary-key collision.
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Saving changes to objects
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Saving changes to objects
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=========================
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=========================
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``save()``
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To save changes to an object that's already in the database, use ``save()``.
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----------
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Use the ``save()`` method to save an object to the database after making
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Given a ``Blog`` instance ``b5`` that has already been saved to the database,
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changes to it::
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this example changes its name and updates its record in the database::
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newblog.name = "Brave New World"
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b5.name = 'New name'
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newblog.save()
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b5.save()
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This performs an ``UPDATE`` SQL statement behind the scenes (see the
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This performs an ``UPDATE`` SQL statement behind the scenes. Django doesn't hit
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`How Django knows to UPDATE vs. INSERT`_ section below). Django doesn't hit
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the database until you explicitly call ``save()``.
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the database until you explicitly call ``save()``.
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The ``save()`` method has no return value.
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The ``save()`` method has no return value.
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``update(**kwargs)``
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--------------------
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**New in Django development version**
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A convenience method for updating and saving an object all in one step, where
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(``**kwargs``) are the attributes to update. Like ``save()``, the
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``update()`` method has no return value.
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Using ``update()``, the above code example could be rewritten as::
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newblog.update(name="Brave New World")
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Since ``update()`` calls ``save()`` behind the scenes, Django will hit the
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database every time ``update()`` is called.
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How Django knows to UPDATE vs. INSERT
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How Django knows to UPDATE vs. INSERT
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-------------------------------------
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-------------------------------------
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@ -802,54 +784,6 @@ has a side effect on your data. For more, see `Safe methods`_ in the HTTP spec.
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.. _Safe methods: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
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.. _Safe methods: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
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``update_or_create(**kwargs)``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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**New in Django development version**
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A convenience method for looking up an object with the given kwargs, and then
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either updating the values of the object if one is found or creating an
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object if one was not found.
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This method calls ``get_or_create()`` behind the scenes, and similarly
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returns a tuple of ``(object, created)``, where``object`` is the updated or
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created object and ``created`` is a boolean specifying whether a new object
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was created.
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This is meant as a shortcut to the following type of code::
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obj, created = Person.objects.get_or_create(first_name='John', last_name='Lennon',
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defaults={'birthday': date(1940, 10, 9)})
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if not created:
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obj.update('birthday'=date(1940, 10, 9))
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This pattern gets quite unwieldy as the number of fields in a model goes up.
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The above example can be rewritten using ``update_or_create()`` like so::
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obj, created = Person.objects.update_or_create(first_name='John', last_name='Lennon',
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defaults={'birthday': date(1940, 10, 9)})
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Any keyword arguments passed to ``update_or_create()`` will be used in a
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call to ``get_or_create()``. If ``get_or_create()`` creates an object, then
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nothing needs to be done by ``update_or_create()`` and a tuple of the created
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object and ``True`` is returned. If, on the other hand, ``get_or_create()``
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does not create a new object, then ``update_or_create()`` will update the
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object with the values passed in the ``defaults`` parameter and a tuple of
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the updated object and ``True`` is returned.
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The ``defaults`` parameter should be a dict of attribute-value pairs that
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you want to update. If ``defaults`` is empty or not specified, then
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``update_or_create()`` will act exactly like ``get_or_create()`` since there
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would be nothing to update.
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As with ``get_or_create()``, if you need to use ``update_or_create()`` in a
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view, please make sure to use it only in ``POST`` requests unless you have a
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good reason not to. ``GET`` requests shouldn't have any effect on data; use
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``POST`` whenever a request to a page has a side effect on your data. For
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more, see `Safe methods`_ in the HTTP spec.
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.. _Safe methods: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
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``count()``
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``count()``
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~~~~~~~~~~~
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~~~~~~~~~~~
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