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-rw-r--r--docs/db-api.txt60
1 files changed, 59 insertions, 1 deletions
diff --git a/docs/db-api.txt b/docs/db-api.txt
index 3624620609..5108949184 100644
--- a/docs/db-api.txt
+++ b/docs/db-api.txt
@@ -559,7 +559,7 @@ following models::
# ...
hometown = models.ForeignKey(City)
- class Book(meta.Model):
+ class Book(models.Model):
# ...
author = models.ForeignKey(Person)
@@ -705,6 +705,64 @@ The ``DoesNotExist`` exception inherits from
except ObjectDoesNotExist:
print "Either the entry or blog doesn't exist."
+``get_or_create(**kwargs)``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A convenience method for looking up an object with the given kwargs, creating
+one if necessary.
+
+Returns a tuple of ``(object, created)``, where ``object`` is the retrieved or
+created object and ``created`` is a boolean specifying whether a new object was
+created.
+
+This is meant as a shortcut to boilerplatish code and is mostly useful for
+data-import scripts. For example::
+
+ try:
+ obj = Person.objects.get(first_name='John', last_name='Lennon')
+ except Person.DoesNotExist:
+ obj = Person(first_name='John', last_name='Lennon', birthday=date(1940, 10, 9))
+ obj.save()
+
+This pattern gets quite unwieldy as the number of fields in a model goes up.
+The above example can be rewritten using ``get_or_create()`` like so::
+
+ obj, created = Person.objects.get_or_create(first_name='John', last_name='Lennon',
+ defaults={'birthday': date(1940, 10, 9)})
+
+Any keyword arguments passed to ``get_or_create()`` -- *except* an optional one
+called ``defaults`` -- will be used in a ``get()`` call. If an object is found,
+``get_or_create()`` returns a tuple of that object and ``False``. If an object
+is *not* found, ``get_or_create()`` will instantiate and save a new object,
+returning a tuple of the new object and ``True``. The new object will be
+created according to this algorithm::
+
+ defaults = kwargs.pop('defaults', {})
+ params = dict([(k, v) for k, v in kwargs.items() if '__' not in k])
+ params.update(defaults)
+ obj = self.model(**params)
+ obj.save()
+
+In English, that means start with any non-``'defaults'`` keyword argument that
+doesn't contain a double underscore (which would indicate a non-exact lookup).
+Then add the contents of ``defaults``, overriding any keys if necessary, and
+use the result as the keyword arguments to the model class.
+
+If you have a field named ``defaults`` and want to use it as an exact lookup in
+``get_or_create()``, just use ``'defaults__exact'``, like so::
+
+ Foo.objects.get_or_create(defaults__exact='bar', defaults={'defaults': 'baz'})
+
+Finally, a word on using ``get_or_create()`` in Django views. As mentioned
+earlier, ``get_or_create()`` is mostly useful in scripts that need to parse
+data and create new records if existing ones aren't available. But if you need
+to use ``get_or_create()`` in a view, please make sure to use it only in
+``POST`` requests unless you have a good reason not to. ``GET`` requests
+shouldn't have any effect on data; use ``POST`` whenever a request to a page
+has a side effect on your data. For more, see `Safe methods`_ in the HTTP spec.
+
+.. _Safe methods: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
+
``count()``
~~~~~~~~~~~