Fixed #14120 - Document get() in Making Queries - thanks danielr and adamv for work on the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14820 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Timo Graham 2010-12-04 22:32:01 +00:00
parent 097072aee4
commit 111ed0195e
1 changed files with 38 additions and 6 deletions

View File

@ -163,6 +163,7 @@ That's because ``Entry.objects``, the root ``QuerySet``, is a special case
that cannot be evaluated. The ``all()`` method returns a ``QuerySet`` that that cannot be evaluated. The ``all()`` method returns a ``QuerySet`` that
*can* be evaluated.) *can* be evaluated.)
Retrieving specific objects with filters Retrieving specific objects with filters
---------------------------------------- ----------------------------------------
@ -258,12 +259,43 @@ aren't fetched from the database until you "ask" for them. When you do, the
``QuerySet`` is *evaluated* by accessing the database. For more details on ``QuerySet`` is *evaluated* by accessing the database. For more details on
exactly when evaluation takes place, see :ref:`when-querysets-are-evaluated`. exactly when evaluation takes place, see :ref:`when-querysets-are-evaluated`.
Other QuerySet methods
~~~~~~~~~~~~~~~~~~~~~~
Most of the time you'll use ``all()``, ``filter()`` and ``exclude()`` when you .. _retrieving-single-object-with-get:
need to look up objects from the database. However, that's far from all there is; see the :ref:`QuerySet API Reference <queryset-api>` for a complete list
of all the various ``QuerySet`` methods. Retrieving a single object with get
-----------------------------------
``.filter()`` will always give you a ``QuerySet``, even if only a single
object matches the query - in this case, it will be a ``QuerySet`` containing
a single element.
If you know there is only one object that matches your query, you can use
the ``get()`` method on a `Manager` which returns the object directly::
>>> one_entry = Entry.objects.get(pk=1)
You can use any query expression with ``get()``, just like with ``filter()`` -
again, see `Field lookups`_ below.
Note that there is a difference between using ``.get()``, and using
``.filter()`` with a slice of ``[0]``. If there are no results that match the
query, ``.get()`` will raise a ``DoesNotExist`` exception. This exception is an
attribute of the model class that the query is being performed on - so in the
code above, if there is no ``Entry`` object with a primary key of 1, Django will
raise ``Entry.DoesNotExist``.
Similarly, Django will complain if more than one item matches the ``get()``
query. In this case, it will raise ``MultipleObjectsReturned``, which again is
an attribute of the model class itself.
Other QuerySet methods
----------------------
Most of the time you'll use ``all()``, ``get()``, ``filter()`` and ``exclude()``
when you need to look up objects from the database. However, that's far from all
there is; see the :ref:`QuerySet API Reference <queryset-api>` for a complete
list of all the various ``QuerySet`` methods.
.. _limiting-querysets: .. _limiting-querysets:
@ -304,7 +336,7 @@ This is roughly equivalent to::
Note, however, that the first of these will raise ``IndexError`` while the Note, however, that the first of these will raise ``IndexError`` while the
second will raise ``DoesNotExist`` if no objects match the given criteria. See second will raise ``DoesNotExist`` if no objects match the given criteria. See
``get()`` for more details. :meth:`~django.db.models.QuerySet.get` for more details.
.. _field-lookups-intro: .. _field-lookups-intro: