====================================

Writing custom django-admin commands

====================================

.. versionadded:: 1.0

Applications can register their own actions with ``manage.py``. For example,

you might want to add a ``manage.py`` action for a Django app that you're

distributing. In this document, we will be building a custom ``closepoll``

command for the ``polls`` application from the

:doc:`tutorial</intro/tutorial01>`.

To do this, just add a ``management/commands`` directory to the application.

Each Python module in that directory will be auto-discovered and registered as

a command that can be executed as an action when you run ``manage.py``::

    polls/

        __init__.py

        models.py

        management/

            __init__.py

            commands/

                __init__.py

                closepoll.py

        tests.py

        views.py

In this example, the ``closepoll`` command will be made available to any project

that includes the ``polls`` application in :setting:`INSTALLED_APPS`.

The ``closepoll.py`` module has only one requirement -- it must define a class

``Command`` that extends :class:`BaseCommand` or one of its

:ref:`subclasses<ref-basecommand-subclasses>`.

.. admonition:: Standalone scripts

  Custom management commands are especially useful for running standalone

  scripts or for scripts that are periodically executed from the UNIX crontab

  or from Windows scheduled tasks control panel.

To implement the command, edit ``polls/management/commands/closepoll.py`` to

look like this:

.. code-block:: python

    from django.core.management.base import BaseCommand, CommandError

    from example.polls.models import Poll

    class Command(BaseCommand):

        args = '<poll_id poll_id ...>'

        help = 'Closes the specified poll for voting'

        def handle(self, *args, **options):

            for poll_id in args:

                try:

                    poll = Poll.objects.get(pk=int(poll_id))

                except Poll.DoesNotExist:

                    raise CommandError('Poll "%s" does not exist' % poll_id)

                poll.opened = False

                poll.save()

                print 'Successfully closed poll "%s"' % poll_id

The new custom command can be called using ``python manage.py closepoll

<poll_id>``.

The ``handle()`` method takes zero or more ``poll_ids`` and sets ``poll.opened``

to ``False`` for each one. If the user referenced any nonexistant polls, a

:class:`CommandError` is raised. The ``poll.opened`` attribute does not exist

in the :doc:`tutorial</intro/tutorial01>` and was added to

``polls.models.Poll`` for this example.

The same ``closepoll`` could be easily modified to delete a given poll instead

of closing it by accepting additional command line options. These custom options

must be added to :attr:`~BaseCommand.option_list` like this:

.. code-block:: python

    from optparse import make_option

    class Command(BaseCommand):

        option_list = BaseCommand.option_list + (

            make_option('--delete',

                action='store_true',

                dest='delete',

                default=False,

                help='Delete poll instead of closing it'),

            )

        # ...

In addition to being able to add custom command line options, all

:doc:`management commands</ref/django-admin>` can accept some

default options such as :djadminopt:`--verbosity` and :djadminopt:`--traceback`.

Command objects

===============

.. class:: BaseCommand

The base class from which all management commands ultimately derive.

Use this class if you want access to all of the mechanisms which

parse the command-line arguments and work out what code to call in

response; if you don't need to change any of that behavior,

consider using one of its :ref:`subclasses<ref-basecommand-subclasses>`.

Subclassing the :class:`BaseCommand` class requires that you implement the

:meth:`~BaseCommand.handle` method.

Attributes

----------

All attributes can be set in your derived class and can be used in

:class:`BaseCommand`'s :ref:`subclasses<ref-basecommand-subclasses>`.

.. attribute:: BaseCommand.args

  A string listing the arguments accepted by the command,

  suitable for use in help messages; e.g., a command which takes

  a list of application names might set this to '<appname

  appname ...>'.

.. attribute:: BaseCommand.can_import_settings

  A boolean indicating whether the command needs to be able to

  import Django settings; if ``True``, ``execute()`` will verify

  that this is possible before proceeding. Default value is

  ``True``.

.. attribute:: BaseCommand.help

  A short description of the command, which will be printed in the

  help message when the user runs the command

  ``python manage.py help <command>``.

.. attribute:: BaseCommand.option_list

  This is the list of ``optparse`` options which will be fed

  into the command's ``OptionParser`` for parsing arguments.

.. attribute:: BaseCommand.output_transaction

  A boolean indicating whether the command outputs SQL

  statements; if ``True``, the output will automatically be

  wrapped with ``BEGIN;`` and ``COMMIT;``. Default value is

  ``False``.

.. attribute:: BaseCommand.requires_model_validation

  A boolean; if ``True``, validation of installed models will be

  performed prior to executing the command. Default value is

  ``True``. To validate an individual application's models

  rather than all applications' models, call

  :meth:`~BaseCommand.validate` from :meth:`~BaseCommand.handle`.

Methods

-------

:class:`BaseCommand` has a few methods that can be overridden but only

the :meth:`~BaseCommand.handle` method must be implemented.

.. admonition:: Implementing a constructor in a subclass

  If you implement ``__init__`` in your subclass of :class:`BaseCommand`,

  you must call :class:`BaseCommand`'s ``__init__``.

  .. code-block:: python

    class Command(BaseCommand):

        def __init__(self, *args, **kwargs):

            super(Command, self).__init__(*args, **kwargs)

            # ...

.. method:: BaseCommand.get_version()

    Return the Django version, which should be correct for all

    built-in Django commands. User-supplied commands can

    override this method to return their own version.

.. method:: BaseCommand.execute(*args, **options)

    Try to execute this command, performing model validation if

    needed (as controlled by the attribute

    :attr:`requires_model_validation`). If the command raises a

    :class:`CommandError`, intercept it and print it sensibly to

    stderr.

.. method:: BaseCommand.handle(*args, **options)

    The actual logic of the command. Subclasses must implement this method.

.. _ref-basecommand-subclasses:

BaseCommand subclasses

----------------------

.. class:: AppCommand

A management command which takes one or more installed application

names as arguments, and does something with each of them.

Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement

:meth:`~AppCommand.handle_app`, which will be called once for each application.

.. method:: AppCommand.handle_app(app, **options)

    Perform the command's actions for ``app``, which will be the

    Python module corresponding to an application name given on

    the command line.

.. class:: LabelCommand

A management command which takes one or more arbitrary arguments

(labels) on the command line, and does something with each of

them.

Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement

:meth:`~LabelCommand.handle_label`, which will be called once for each label.

.. method:: LabelCommand.handle_label(label, **options)

    Perform the command's actions for ``label``, which will be the

    string as given on the command line.

.. class:: NoArgsCommand

A command which takes no arguments on the command line.

Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement

:meth:`~NoArgsCommand.handle_noargs`; :meth:`~BaseCommand.handle` itself is

overridden to ensure no arguments are passed to the command.

.. method:: NoArgsCommand.handle_noargs(**options)

    Perform this command's actions

.. _ref-command-exceptions:

Command exceptions

------------------

.. class:: CommandError

Exception class indicating a problem while executing a management

command.

If this exception is raised during the execution of a management

command, it will be caught and turned into a nicely-printed error

message to the appropriate output stream (i.e., stderr); as a

result, raising this exception (with a sensible description of the

error) is the preferred way to indicate that something has gone

wrong in the execution of a command.