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Fixed #9170 -- added improved custom management command documentation. 

Thanks to David Fischer and Eric Holscher for their work on initial patches.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13138 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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Brian Rosner 2010-05-08 21:38:00 +00:00
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docs/howto/custom-management-commands.txt
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.. _howto-custom-management-commands:
====================================
Writing custom django-admin commands
====================================
@ -7,27 +8,248 @@ Writing custom django-admin commands
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.
distributing. In this document, we will be building a custom ``closepoll``
command for the ``polls`` application from the
:ref:`tutorial<intro-tutorial01>`.
To do this, just add a ``management/commands`` directory to your application.
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``::
blog/
polls/
__init__.py
models.py
management/
__init__.py
commands/
__init__.py
explode.py
closepoll.py
tests.py
views.py
In this example, the ``explode`` command will be made available to any project
that includes the ``blog`` application in ``settings.INSTALLED_APPS``.
In this example, the ``closepoll`` command will be made available to any project
that includes the ``polls`` application in :setting:`INSTALLED_APPS`.
The ``explode.py`` module has only one requirement -- it must define a class
called ``Command`` that extends ``django.core.management.base.BaseCommand``.
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>`.
For more details on how to define your own commands, look at the code for the
existing ``django-admin.py`` commands, in ``/django/core/management/commands``.
.. 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 :ref:`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
:ref:`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.