django “如何”系列2：如何编写django-admin 命令

àì夳堔傛蜴生んèń 2023-06-04 05:51 119阅读 0赞

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。

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][]

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()

BaseCommand

转载于:https://www.cnblogs.com/qwj-sysu/p/4230582.html

[ContractedBlock.gif]: https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif
[ExpandedBlockStart.gif]: /images/20230601/41a94db82e9f4aec8ac8d5408444bc88.png