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307 lines
11 KiB
Text
307 lines
11 KiB
Text
====================================
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Writing custom django-admin commands
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====================================
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Applications can register their own actions with ``manage.py``. For example,
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you might want to add a ``manage.py`` action for a Django app that you're
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distributing. In this document, we will be building a custom ``closepoll``
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command for the ``polls`` application from the
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:doc:`tutorial</intro/tutorial01>`.
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To do this, just add a ``management/commands`` directory to the application.
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Each Python module in that directory will be auto-discovered and registered as
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a command that can be executed as an action when you run ``manage.py``::
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polls/
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__init__.py
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models.py
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management/
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__init__.py
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commands/
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__init__.py
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closepoll.py
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tests.py
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views.py
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In this example, the ``closepoll`` command will be made available to any project
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that includes the ``polls`` application in :setting:`INSTALLED_APPS`.
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The ``closepoll.py`` module has only one requirement -- it must define a class
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``Command`` that extends :class:`BaseCommand` or one of its
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:ref:`subclasses<ref-basecommand-subclasses>`.
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.. admonition:: Standalone scripts
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Custom management commands are especially useful for running standalone
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scripts or for scripts that are periodically executed from the UNIX crontab
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or from Windows scheduled tasks control panel.
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To implement the command, edit ``polls/management/commands/closepoll.py`` to
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look like this:
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.. code-block:: python
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from django.core.management.base import BaseCommand, CommandError
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from example.polls.models import Poll
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class Command(BaseCommand):
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args = '<poll_id poll_id ...>'
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help = 'Closes the specified poll for voting'
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def handle(self, *args, **options):
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for poll_id in args:
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try:
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poll = Poll.objects.get(pk=int(poll_id))
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except Poll.DoesNotExist:
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raise CommandError('Poll "%s" does not exist' % poll_id)
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poll.opened = False
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poll.save()
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self.stdout.write('Successfully closed poll "%s"\n' % poll_id)
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.. note::
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When you are using management commands and wish to provide console
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output, you should write to ``self.stdout`` and ``self.stderr``,
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instead of printing to ``stdout`` and ``stderr`` directly. By
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using these proxies, it becomes much easier to test your custom
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command.
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The new custom command can be called using ``python manage.py closepoll
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<poll_id>``.
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The ``handle()`` method takes zero or more ``poll_ids`` and sets ``poll.opened``
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to ``False`` for each one. If the user referenced any nonexistent polls, a
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:class:`CommandError` is raised. The ``poll.opened`` attribute does not exist
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in the :doc:`tutorial</intro/tutorial01>` and was added to
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``polls.models.Poll`` for this example.
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The same ``closepoll`` could be easily modified to delete a given poll instead
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of closing it by accepting additional command line options. These custom options
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must be added to :attr:`~BaseCommand.option_list` like this:
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.. code-block:: python
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from optparse import make_option
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class Command(BaseCommand):
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option_list = BaseCommand.option_list + (
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make_option('--delete',
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action='store_true',
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dest='delete',
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default=False,
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help='Delete poll instead of closing it'),
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)
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# ...
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In addition to being able to add custom command line options, all
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:doc:`management commands</ref/django-admin>` can accept some
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default options such as :djadminopt:`--verbosity` and :djadminopt:`--traceback`.
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.. admonition:: Management commands and locales
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The :meth:`BaseCommand.execute` method sets the hardcoded ``en-us`` locale
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because the commands shipped with Django perform several tasks
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(for example, user-facing content rendering and database population) that
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require a system-neutral string language (for which we use ``en-us``).
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If your custom management command uses another locale, you should manually
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activate and deactivate it in your :meth:`~BaseCommand.handle` or
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:meth:`~NoArgsCommand.handle_noargs` method using the functions provided by
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the I18N support code:
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.. code-block:: python
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from django.core.management.base import BaseCommand, CommandError
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from django.utils import translation
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class Command(BaseCommand):
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...
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self.can_import_settings = True
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def handle(self, *args, **options):
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# Activate a fixed locale, e.g. Russian
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translation.activate('ru')
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# Or you can activate the LANGUAGE_CODE
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# chosen in the settings:
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#
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#from django.conf import settings
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#translation.activate(settings.LANGUAGE_CODE)
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# Your command logic here
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# ...
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translation.deactivate()
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Take into account though, that system management commands typically have to
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be very careful about running in non-uniform locales, so:
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* Make sure the :setting:`USE_I18N` setting is always ``True`` when running
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the command (this is one good example of the potential problems stemming
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from a dynamic runtime environment that Django commands avoid offhand by
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always using a fixed locale).
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* Review the code of your command and the code it calls for behavioral
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differences when locales are changed and evaluate its impact on
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predictable behavior of your command.
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Command objects
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===============
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.. class:: BaseCommand
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The base class from which all management commands ultimately derive.
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Use this class if you want access to all of the mechanisms which
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parse the command-line arguments and work out what code to call in
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response; if you don't need to change any of that behavior,
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consider using one of its :ref:`subclasses<ref-basecommand-subclasses>`.
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Subclassing the :class:`BaseCommand` class requires that you implement the
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:meth:`~BaseCommand.handle` method.
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Attributes
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----------
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All attributes can be set in your derived class and can be used in
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:class:`BaseCommand`'s :ref:`subclasses<ref-basecommand-subclasses>`.
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.. attribute:: BaseCommand.args
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A string listing the arguments accepted by the command,
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suitable for use in help messages; e.g., a command which takes
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a list of application names might set this to '<appname
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appname ...>'.
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.. attribute:: BaseCommand.can_import_settings
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A boolean indicating whether the command needs to be able to
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import Django settings; if ``True``, ``execute()`` will verify
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that this is possible before proceeding. Default value is
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``True``.
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.. attribute:: BaseCommand.help
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A short description of the command, which will be printed in the
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help message when the user runs the command
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``python manage.py help <command>``.
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.. attribute:: BaseCommand.option_list
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This is the list of ``optparse`` options which will be fed
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into the command's ``OptionParser`` for parsing arguments.
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.. attribute:: BaseCommand.output_transaction
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A boolean indicating whether the command outputs SQL
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statements; if ``True``, the output will automatically be
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wrapped with ``BEGIN;`` and ``COMMIT;``. Default value is
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``False``.
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.. attribute:: BaseCommand.requires_model_validation
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A boolean; if ``True``, validation of installed models will be
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performed prior to executing the command. Default value is
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``True``. To validate an individual application's models
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rather than all applications' models, call
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:meth:`~BaseCommand.validate` from :meth:`~BaseCommand.handle`.
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Methods
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-------
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:class:`BaseCommand` has a few methods that can be overridden but only
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the :meth:`~BaseCommand.handle` method must be implemented.
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.. admonition:: Implementing a constructor in a subclass
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If you implement ``__init__`` in your subclass of :class:`BaseCommand`,
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you must call :class:`BaseCommand`'s ``__init__``.
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.. code-block:: python
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class Command(BaseCommand):
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def __init__(self, *args, **kwargs):
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super(Command, self).__init__(*args, **kwargs)
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# ...
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.. method:: BaseCommand.get_version()
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Return the Django version, which should be correct for all
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built-in Django commands. User-supplied commands can
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override this method to return their own version.
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.. method:: BaseCommand.execute(*args, **options)
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Try to execute this command, performing model validation if
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needed (as controlled by the attribute
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:attr:`requires_model_validation`). If the command raises a
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:class:`CommandError`, intercept it and print it sensibly to
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stderr.
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.. method:: BaseCommand.handle(*args, **options)
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The actual logic of the command. Subclasses must implement this method.
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.. _ref-basecommand-subclasses:
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BaseCommand subclasses
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----------------------
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.. class:: AppCommand
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A management command which takes one or more installed application
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names as arguments, and does something with each of them.
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Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement
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:meth:`~AppCommand.handle_app`, which will be called once for each application.
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.. method:: AppCommand.handle_app(app, **options)
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Perform the command's actions for ``app``, which will be the
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Python module corresponding to an application name given on
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the command line.
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.. class:: LabelCommand
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A management command which takes one or more arbitrary arguments
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(labels) on the command line, and does something with each of
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them.
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Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement
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:meth:`~LabelCommand.handle_label`, which will be called once for each label.
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.. method:: LabelCommand.handle_label(label, **options)
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Perform the command's actions for ``label``, which will be the
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string as given on the command line.
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.. class:: NoArgsCommand
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A command which takes no arguments on the command line.
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Rather than implementing :meth:`~BaseCommand.handle`, subclasses must implement
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:meth:`~NoArgsCommand.handle_noargs`; :meth:`~BaseCommand.handle` itself is
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overridden to ensure no arguments are passed to the command.
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.. method:: NoArgsCommand.handle_noargs(**options)
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Perform this command's actions
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.. _ref-command-exceptions:
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Command exceptions
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------------------
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.. class:: CommandError
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Exception class indicating a problem while executing a management
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command.
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If this exception is raised during the execution of a management
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command, it will be caught and turned into a nicely-printed error
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message to the appropriate output stream (i.e., stderr); as a
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result, raising this exception (with a sensible description of the
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error) is the preferred way to indicate that something has gone
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wrong in the execution of a command.
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