Django2.0手册:Writing custom



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
tutorial.

To do this, just add a management/commands directory to the application.
Django will register a manage.py command for each Python module in that
directory whose name doesn’t begin with an underscore. For example:

polls/
    __init__.py
    models.py
    management/
        __init__.py
        commands/
            __init__.py
            _private.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 INSTALLED_APPS.

The _private.py module will not be available as a management command.

The closepoll.py module has only one requirement — it must define a class
Command that extends BaseCommand or one of its
subclasses.

独一无二的脚本

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:

from django.core.management.base import BaseCommand, CommandError
from polls.models import Question as Poll

class Command(BaseCommand):
    help = 'Closes the specified poll for voting'

    def add_arguments(self, parser):
        parser.add_argument('poll_id', nargs='+', type=int)

    def handle(self, *args, **options):
        for poll_id in options['poll_id']:
            try:
                poll = Poll.objects.get(pk=poll_id)
            except Poll.DoesNotExist:
                raise CommandError('Poll "%s" does not exist' % poll_id)

            poll.opened = False
            poll.save()

            self.stdout.write(self.style.SUCCESS('Successfully closed poll "%s"' % poll_id))

Note

When you are using management commands and wish to provide console
output, you should write to self.stdout and self.stderr,
instead of printing to stdout and stderr directly. By
using these proxies, it becomes much easier to test your custom
command. Note also that you don’t need to end messages with a newline
character, it will be added automatically, unless you specify the ending
parameter:

self.stdout.write("Unterminated line", ending='')

The new custom command can be called using python manage.py closepoll
<poll_id>
.

The handle() method takes one or more poll_ids and sets poll.opened
to False for each one. If the user referenced any nonexistent polls, a
CommandError is raised. The poll.opened attribute does not exist in
the tutorial and was added to
polls.models.Question for this example.

接受可选参数¶

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 can be added in the add_arguments() method like this:

class Command(BaseCommand):
    def add_arguments(self, parser):
        # Positional arguments
        parser.add_argument('poll_id', nargs='+', type=int)

        # Named (optional) arguments
        parser.add_argument(
            '--delete',
            action='store_true',
            dest='delete',
            help='Delete poll instead of closing it',
        )

    def handle(self, *args, **options):
        # ...
        if options['delete']:
            poll.delete()
        # ...

The option (delete in our example) is available in the options dict
parameter of the handle method. See the argparse Python documentation
for more about add_argument usage.

In addition to being able to add custom command line options, all
management commands can accept some default options
such as --verbosity and --traceback.

Management commands and locales¶

By default, the BaseCommand.execute() method deactivates translations
because some commands shipped with Django perform several tasks (for example,
user-facing content rendering and database population) that require a
project-neutral string language.

If, for some reason, your custom management command needs to use a fixed locale,
you should manually activate and deactivate it in your
handle() method using the functions provided by the I18N
support code:

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

class Command(BaseCommand):
    ...

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

        # Activate a fixed locale, e.g. Russian
        translation.activate('ru')

        # Or you can activate the LANGUAGE_CODE # chosen in the settings:
        from django.conf import settings
        translation.activate(settings.LANGUAGE_CODE)

        # Your command logic here
        ...

        translation.deactivate()

Another need might be that your command simply should use the locale set in
settings and Django should be kept from deactivating it. You can achieve
it by using the BaseCommand.leave_locale_alone option.

When working on the scenarios described above though, take into account that
system management commands typically have to be very careful about running in
non-uniform locales, so you might need to:

  • Make sure the USE_I18N setting is always True when running
    the command (this is a good example of the potential problems stemming
    from a dynamic runtime environment that Django commands avoid offhand by
    deactivating translations).
  • Review the code of your command and the code it calls for behavioral
    differences when locales are changed and evaluate its impact on
    predictable behavior of your command.

测试中¶

Information on how to test custom management commands can be found in the
testing docs.

覆盖命令¶

Django 先注册内置命令, 然后按相反的顺序在 INSTALLED_APPS 查找命令. 在查找时, 如果一个命令和已注册的命令重名, 这个新发现的命令会覆盖第一个命令.

换句话说, 为了覆盖一个命令, 新命令必须有同样的名字并且它的 app 在 INSTALLED_APPS 中必须排在被覆盖命令 app 的前面.

Management commands from third-party apps that have been unintentionally
overridden can be made available under a new name by creating a new command in
one of your project’s apps (ordered before the third-party app in
INSTALLED_APPS) which imports the Command of the overridden
command.

命令对象¶

class BaseCommand[source]

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 subclasses.

Subclassing the BaseCommand class requires that you implement the
handle() method.

属性¶

All attributes can be set in your derived class and can be used in
BaseCommand’s subclasses.

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>.

BaseCommand.missing_args_message

If your command defines mandatory positional arguments, you can customize
the message error returned in the case of missing arguments. The default is
output by argparse (“too few arguments”).

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.

BaseCommand.requires_migrations_checks

A boolean; if True, the command prints a warning if the set of
migrations on disk don’t match the migrations in the database. A warning
doesn’t prevent the command from executing. Default value is False.

BaseCommand.requires_system_checks

A boolean; if True, the entire Django project will be checked for
potential problems prior to executing the command. Default value is True.

BaseCommand.leave_locale_alone

A boolean indicating whether the locale set in settings should be preserved
during the execution of the command instead of translations being
deactivated.

默认值是 False

Make sure you know what you are doing if you decide to change the value of
this option in your custom command if it creates database content that
is locale-sensitive and such content shouldn’t contain any translations
(like it happens e.g. with django.contrib.auth permissions) as
activating any locale might cause unintended effects. See the Management
commands and locales
section above for further details.

BaseCommand.style

An instance attribute that helps create colored output when writing to
stdout or stderr. For example:

self.stdout.write(self.style.SUCCESS('...'))

See Syntax coloring to learn how to modify the color palette and to
see the available styles (use uppercased versions of the “roles” described
in that section).

If you pass the --no-color option when running your command, all
self.style() calls will return the original string uncolored.

方法¶

BaseCommand has a few methods that can be overridden but only
the handle() method must be implemented.

Implementing a constructor in a subclass

If you implement __init__ in your subclass of BaseCommand,
you must call BaseCommand’s __init__:

class Command(BaseCommand):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # ...
BaseCommand.add_arguments(parser)[source]

Entry point to add parser arguments to handle command line arguments passed
to the command. Custom commands should override this method to add both
positional and optional arguments accepted by the command. Calling
super() is not needed when directly subclassing BaseCommand.

BaseCommand.get_version()[source]

Returns 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.

BaseCommand.execute(*args, **options)[source]

Tries to execute this command, performing system checks if needed (as
controlled by the requires_system_checks attribute). If the command
raises a CommandError, it’s intercepted and printed to stderr.

在你的代码中调用管理命令

execute() should not be called directly from your code to execute a
command. Use call_command() instead.

BaseCommand.handle(*args, **options)[source]

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

It may return a string which will be printed to stdout (wrapped
by BEGIN; and COMMIT; if output_transaction is True).

BaseCommand.check(app_configs=None, tags=None, display_num_errors=False)[source]

Uses the system check framework to inspect the entire Django project for
potential problems. Serious problems are raised as a CommandError;
warnings are output to stderr; minor notifications are output to stdout.

If app_configs and tags are both None, all system checks are
performed. tags can be a list of check tags, like compatibility or
models.

BaseCommand subclasses¶

class AppCommand

A management command which takes one or more installed application labels as
arguments, and does something with each of them.

Rather than implementing handle(), subclasses must
implement handle_app_config(), which will be called once for
each application.

AppCommand.handle_app_config(app_config, **options)

Perform the command’s actions for app_config, which will be an
AppConfig instance corresponding to an application
label 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 handle(), subclasses must implement
handle_label(), which will be called once for each label.

LabelCommand.label

A string describing the arbitrary arguments passed to the command. The
string is used in the usage text and error messages of the command.
Defaults to 'label'.

LabelCommand.handle_label(label, **options)

Perform the command’s actions for label, which will be the string as
given on the command line.

命令异常¶

exception CommandError[source]

Exception class indicating a problem while executing a management command.

If this exception is raised during the execution of a management command from a
command line console, 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.

If a management command is called from code through
call_command(), it’s up to you to catch the
exception when needed.