django “如何”系列2:如何编写django-admin 命令
应用可以使用manage.py注册自己的动作,例如,你可能想要为你即将发布的应用添加一个manage.py 操作。这节我们将为polls应用添加一个closepoll的命令
添加一个management/commands目录如下
- polls/
- __init__.py
- models.py
- management/
- __init__.py
- commands/
- __init__.py
- _private.py
- closepoll.py
- tests.py
- views.py
这样添加之后,任何包含polls在INSTALLED_APPS的项目都可以使用closepoll命令
_private.py模块不会作为一个管理命令
closepoll.py模块有一个要求--必须定义一个类Command拓展或者继承BaseCommand
下面是这个命令的一个实例实现(closepoll.py)
- 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()
- self.stdout.write('Successfully closed poll "%s"\n' % poll_id)
注意:使用self.stdout和self.stderr而不是stdout和stderr
这个新命令的可以通过python manage.py closepoll <poll_id>来调用
更多更详细的关于BaseCommand的代码附于下面:常用到的参数是args(参数格式说明)和help(命令说明),必须实现的方法是handle(如何实现这个命令),正如上面的例子的那样,如果没有特别的要求,下面的代码其实不用看了。
- class BaseCommand(object):
- """
- 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 the subclasses defined in this file.
- If you are interested in overriding/customizing various aspects of
- the command-parsing and -execution behavior, the normal flow works
- as follows:
- 1. ``django-admin.py`` or ``manage.py`` loads the command class
- and calls its ``run_from_argv()`` method.
- 2. The ``run_from_argv()`` method calls ``create_parser()`` to get
- an ``OptionParser`` for the arguments, parses them, performs
- any environment changes requested by options like
- ``pythonpath``, and then calls the ``execute()`` method,
- passing the parsed arguments.
- 3. The ``execute()`` method attempts to carry out the command by
- calling the ``handle()`` method with the parsed arguments; any
- output produced by ``handle()`` will be printed to standard
- output and, if the command is intended to produce a block of
- SQL statements, will be wrapped in ``BEGIN`` and ``COMMIT``.
- 4. If ``handle()`` raised a ``CommandError``, ``execute()`` will
- instead print an error message to ``stderr``.
- Thus, the ``handle()`` method is typically the starting point for
- subclasses; many built-in commands and command types either place
- all of their logic in ``handle()``, or perform some additional
- parsing work in ``handle()`` and then delegate from it to more
- specialized methods as needed.
- Several attributes affect behavior at various steps along the way:
- ``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 ...>'.
- ``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``.
- ``help``
- A short description of the command, which will be printed in
- help messages.
- ``option_list``
- This is the list of ``optparse`` options which will be fed
- into the command's ``OptionParser`` for parsing arguments.
- ``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``.
- ``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
- ``self.validate(app)`` from ``handle()``, where ``app`` is the
- application's Python module.
- """
- # Metadata about this command.
- option_list = (
- make_option('-v', '--verbosity', action='store', dest='verbosity', default='',
- type='choice', choices=['', '', '', ''],
- help='Verbosity level; 0=minimal output, 1=normal output, 2=verbose output, 3=very verbose output'),
- make_option('--settings',
- help='The Python path to a settings module, e.g. "myproject.settings.main". If this isn\'t provided, the DJANGO_SETTINGS_MODULE environment variable will be used.'),
- make_option('--pythonpath',
- help='A directory to add to the Python path, e.g. "/home/djangoprojects/myproject".'),
- make_option('--traceback', action='store_true',
- help='Print traceback on exception'),
- )
- help = ''
- args = ''
- # Configuration shortcuts that alter various logic.
- can_import_settings = True
- requires_model_validation = True
- output_transaction = False # Whether to wrap the output in a "BEGIN; COMMIT;"
- def __init__(self):
- self.style = color_style()
- def get_version(self):
- """
- Return the Django version, which should be correct for all
- built-in Django commands. User-supplied commands should
- override this method.
- """
- return django.get_version()
- def usage(self, subcommand):
- """
- Return a brief description of how to use this command, by
- default from the attribute ``self.help``.
- """
- usage = '%%prog %s [options] %s' % (subcommand, self.args)
- if self.help:
- return '%s\n\n%s' % (usage, self.help)
- else:
- return usage
- def create_parser(self, prog_name, subcommand):
- """
- Create and return the ``OptionParser`` which will be used to
- parse the arguments to this command.
- """
- return OptionParser(prog=prog_name,
- usage=self.usage(subcommand),
- version=self.get_version(),
- option_list=self.option_list)
- def print_help(self, prog_name, subcommand):
- """
- Print the help message for this command, derived from
- ``self.usage()``.
- """
- parser = self.create_parser(prog_name, subcommand)
- parser.print_help()
- def run_from_argv(self, argv):
- """
- Set up any environment changes requested (e.g., Python path
- and Django settings), then run this command.
- """
- parser = self.create_parser(argv[0], argv[1])
- options, args = parser.parse_args(argv[2:])
- handle_default_options(options)
- self.execute(*args, **options.__dict__)
- def execute(self, *args, **options):
- """
- Try to execute this command, performing model validation if
- needed (as controlled by the attribute
- ``self.requires_model_validation``). If the command raises a
- ``CommandError``, intercept it and print it sensibly to
- stderr.
- """
- show_traceback = options.get('traceback', False)
- # Switch to English, because django-admin.py creates database content
- # like permissions, and those shouldn't contain any translations.
- # But only do this if we can assume we have a working settings file,
- # because django.utils.translation requires settings.
- saved_lang = None
- if self.can_import_settings:
- try:
- from django.utils import translation
- saved_lang = translation.get_language()
- translation.activate('en-us')
- except ImportError, e:
- # If settings should be available, but aren't,
- # raise the error and quit.
- if show_traceback:
- traceback.print_exc()
- else:
- sys.stderr.write(smart_str(self.style.ERROR('Error: %s\n' % e)))
- sys.exit(1)
- try:
- self.stdout = options.get('stdout', sys.stdout)
- self.stderr = options.get('stderr', sys.stderr)
- if self.requires_model_validation:
- self.validate()
- output = self.handle(*args, **options)
- if output:
- if self.output_transaction:
- # This needs to be imported here, because it relies on
- # settings.
- from django.db import connections, DEFAULT_DB_ALIAS
- connection = connections[options.get('database', DEFAULT_DB_ALIAS)]
- if connection.ops.start_transaction_sql():
- self.stdout.write(self.style.SQL_KEYWORD(connection.ops.start_transaction_sql()) + '\n')
- self.stdout.write(output)
- if self.output_transaction:
- self.stdout.write('\n' + self.style.SQL_KEYWORD("COMMIT;") + '\n')
- except CommandError, e:
- if show_traceback:
- traceback.print_exc()
- else:
- self.stderr.write(smart_str(self.style.ERROR('Error: %s\n' % e)))
- sys.exit(1)
- if saved_lang is not None:
- translation.activate(saved_lang)
- def validate(self, app=None, display_num_errors=False):
- """
- Validates the given app, raising CommandError for any errors.
- If app is None, then this will validate all installed apps.
- """
- from django.core.management.validation import get_validation_errors
- try:
- from cStringIO import StringIO
- except ImportError:
- from StringIO import StringIO
- s = StringIO()
- num_errors = get_validation_errors(s, app)
- if num_errors:
- s.seek(0)
- error_text = s.read()
- raise CommandError("One or more models did not validate:\n%s" % error_text)
- if display_num_errors:
- self.stdout.write("%s error%s found\n" % (num_errors, num_errors != 1 and 's' or ''))
- def handle(self, *args, **options):
- """
- The actual logic of the command. Subclasses must implement
- this method.
- """
- raise NotImplementedError()
BaseCommand
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