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='1', type='choice', choices=['0', '1', '2', '3'], 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()
