======================
Model ``Meta`` options
======================

This document explains all the possible :ref:`metadata options
<meta-options>` that you can give your model in its internal ``class
Meta``.

Available ``Meta`` options
==========================

.. currentmodule:: django.db.models

``abstract``
------------

.. attribute:: Options.abstract

If ``True``, this model will be an :ref:`abstract base class <abstract-base-classes>`.

``app_label``
-------------

.. attribute:: Options.app_label

If a model exists outside of the standard :file:`models.py` (for instance, if
the app's models are in submodules of ``myapp.models``), the model must define
which app it is part of::

    app_label = 'myapp'

``db_table``
------------

.. attribute:: Options.db_table

The name of the database table to use for the model::

    db_table = 'music_album'

.. _table-names:

Table names
~~~~~~~~~~~

To save you time, Django automatically derives the name of the database table
from the name of your model class and the app that contains it. A model's
database table name is constructed by joining the model's "app label" -- the
name you used in ``manage.py startapp`` -- to the model's class name, with an
underscore between them.

For example, if you have an app ``bookstore`` (as created by
``manage.py startapp bookstore``), a model defined as ``class Book`` will have
a database table named ``bookstore_book``.

To override the database table name, use the ``db_table`` parameter in
``class Meta``.

If your database table name is an SQL reserved word, or contains characters that
aren't allowed in Python variable names -- notably, the hyphen -- that's OK.
Django quotes column and table names behind the scenes.

``db_tablespace``
-----------------

.. attribute:: Options.db_tablespace

.. versionadded:: 1.0

The name of the database tablespace to use for the model. If the backend doesn't
support tablespaces, this option is ignored.

``get_latest_by``
-----------------

.. attribute:: Options.get_latest_by

The name of a :class:`DateField` or :class:`DateTimeField` in the model. This
specifies the default field to use in your model :class:`Manager`'s
:class:`~QuerySet.latest` method.

Example::

    get_latest_by = "order_date"

See the docs for :meth:`~django.db.models.QuerySet.latest` for more.

``managed``
-----------------------

.. attribute:: Options.managed

.. versionadded:: 1.1

Defaults to ``True``, meaning Django will create the appropriate database
tables in :djadmin:`syncdb` and remove them as part of a :djadmin:`reset`
management command. That is, Django *manages* the database tables' lifecycles.

If ``False``, no database table creation or deletion operations will be
performed for this model. This is useful if the model represents an existing
table or a database view that has been created by some other means. This is
the *only* difference when ``managed`` is ``False``. All other aspects of
model handling are exactly the same as normal. This includes

    1. Adding an automatic primary key field to the model if you don't declare
       it.  To avoid confusion for later code readers, it's recommended to
       specify all the columns from the database table you are modeling when
       using unmanaged models.

    2. If a model with ``managed=False`` contains a
       :class:`~django.db.models.ManyToManyField` that points to another
       unmanaged model, then the intermediate table for the many-to-many join
       will also not be created. However, a the intermediary table between one
       managed and one unmanaged model *will* be created.

       If you need to change this default behavior, create the intermediary
       table as an explicit model (with ``managed`` set as needed) and use the
       :attr:`ManyToManyField.through` attribute to make the relation use your
       custom model.

For tests involving models with ``managed=False``, it's up to you to ensure
the correct tables are created as part of the test setup.

If you're interested in changing the Python-level behavior of a model class,
you *could* use ``managed=False`` and create a copy of an existing model.
However, there's a better approach for that situation: :ref:`proxy-models`.

``order_with_respect_to``
-------------------------

.. attribute:: Options.order_with_respect_to

Marks this object as "orderable" with respect to the given field. This is almost
always used with related objects to allow them to be ordered with respect to a
parent object. For example, if an ``Answer`` relates to a ``Question`` object,
and a question has more than one answer, and the order of answers matters, you'd
do this::

    class Answer(models.Model):
        question = models.ForeignKey(Question)
        # ...

        class Meta:
            order_with_respect_to = 'question'

When ``order_with_respect_to`` is set, two additional methods are provided to
retrieve and to set the order of the related objects: ``get_RELATED_order()``
and ``set_RELATED_order()``, where ``RELATED`` is the lowercased model name. For
example, assuming that a ``Question`` object has multiple related ``Answer``
objects, the list returned contains the primary keys of the related ``Answer``
objects::

    >>> question = Question.objects.get(id=1)
    >>> question.get_answer_order()
    [1, 2, 3]

The order of a ``Question`` object's related ``Answer`` objects can be set by
passing in a list of ``Answer`` primary keys::

    >>> question.set_answer_order([3, 1, 2])

The related objects also get two methods, ``get_next_in_order()`` and
``get_previous_in_order()``, which can be used to access those objects in their
proper order. Assuming the ``Answer`` objects are ordered by ``id``::

    >>> answer = Answer.objects.get(id=2)
    >>> answer.get_next_in_order()
    <Answer: 3>
    >>> answer.get_previous_in_order()
    <Answer: 1>

``ordering``
------------

.. attribute:: Options.ordering

The default ordering for the object, for use when obtaining lists of objects::

    ordering = ['-order_date']

This is a tuple or list of strings. Each string is a field name with an optional
"-" prefix, which indicates descending order. Fields without a leading "-" will
be ordered ascending. Use the string "?" to order randomly.

.. note::

    Regardless of how many fields are in :attr:`~Options.ordering`, the admin
    site uses only the first field.

For example, to order by a ``pub_date`` field ascending, use this::

    ordering = ['pub_date']

To order by ``pub_date`` descending, use this::

    ordering = ['-pub_date']

To order by ``pub_date`` descending, then by ``author`` ascending, use this::

    ordering = ['-pub_date', 'author']

``permissions``
---------------

.. attribute:: Options.permissions

Extra permissions to enter into the permissions table when creating this object.
Add, delete and change permissions are automatically created for each object
that has ``admin`` set. This example specifies an extra permission,
``can_deliver_pizzas``::

    permissions = (("can_deliver_pizzas", "Can deliver pizzas"),)

This is a list or tuple of 2-tuples in the format ``(permission_code,
human_readable_permission_name)``.

``proxy``
---------

.. attribute:: Options.proxy

.. versionadded:: 1.1

If set to ``True``, a model which subclasses another model will be treated as
a :ref:`proxy model <proxy-models>`.

``unique_together``
-------------------

.. attribute:: Options.unique_together

Sets of field names that, taken together, must be unique::

    unique_together = (("driver", "restaurant"),)

This is a list of lists of fields that must be unique when considered together.
It's used in the Django admin and is enforced at the database level (i.e., the
appropriate ``UNIQUE`` statements are included in the ``CREATE TABLE``
statement).

.. versionadded:: 1.0

For convenience, unique_together can be a single list when dealing with a single
set of fields::

    unique_together = ("driver", "restaurant")

``verbose_name``
----------------

.. attribute:: Options.verbose_name

A human-readable name for the object, singular::

    verbose_name = "pizza"

If this isn't given, Django will use a munged version of the class name:
``CamelCase`` becomes ``camel case``.

``verbose_name_plural``
-----------------------

.. attribute:: Options.verbose_name_plural

The plural name for the object::

    verbose_name_plural = "stories"

If this isn't given, Django will use :attr:`~Options.verbose_name` + ``"s"``.
