django：模板标签返回而不是上一次调用

Question

我的代码返回而不是空字符串我之前调用的值。我该如何解决这个问题？

模板标签：

from django.template import Library, Node, resolve_variable
from django.utils.safestring import SafeText
from django.http import QueryDict

register = Library()

"""
The tag generates a parameter string in form '?param1=val1&param2=val2'.
The parameter list is generated by taking all parameters from current
request.GET and optionally overriding them by providing parameters to the tag.

This is a cleaned up version of http://djangosnippets.org/snippets/2105/. It
solves a couple of issues, namely:
"""

class AddGetParameter(Node):
    def __init__(self, values):
        self.values = values

    def render(self, context):
        req = resolve_variable('request', context)
        params = req.GET.copy()

        for key, value in self.values.items():
            parameterValue=value.resolve(context)

            if value == "" and type(parameterValue) is SafeText and len(parameterValue) == 0 and key in params:
                del params[key]
            else:
                params[key] = parameterValue

        resultDict=dict()
        for key in params:
            if len(str(params[key]))>0:
                resultDict[key]=params[key]

        qdict = QueryDict('', mutable=True)
        qdict.update(resultDict)

        urlString=qdict.urlencode()
        print urlString

        if len(urlString) > 0:
            return '?%s' % urlString
        else:
            return ''

@register.tag
def add_get(parser, token):
    pairs = token.split_contents()[1:]
    values = {}
    for pair in pairs:
        s = pair.split('=', 1)
        values[s[0]] = parser.compile_filter(s[1])
    return AddGetParameter(values)

注意：我修改了代码段，以便从网址中删除未设置为“”的变量。

template.html：

{% load add_get_parameter %}
<a href="{% add_get location="7" %}">set</a>
<a href="{% add_get location="" %}">empty</a>

结果：

<a href="?location=7">set</a>
<a href="?location=7">empty</a>

如果我将return ''更改为return "?"，则结果为：

<a href="?location=7">set</a>
<a href="?">empty</a>

但是我怎么能得到一个字符串什么都没有（长度为0的字符串）？我做错了什么？

更新 settings.py：

# Django settings for Roadrunners project.
from django.core.urlresolvers import reverse_lazy
import djcelery

djcelery.setup_loader()
import os
from django.utils.translation import ugettext_lazy as _

gettext = lambda s: s
PROJECT_PATH = os.path.split(os.path.abspath(os.path.dirname(__file__)))[0]
APPLICATION_PATH=os.path.abspath('.')


DEBUG = True
TEMPLATE_DEBUG = DEBUG

MANAGERS = ADMINS

DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.sqlite3', # Add 'postgresql_psycopg2', 'mysql', 'sqlite3' or 'oracle'.
            'NAME': os.path.join(PROJECT_PATH, 'database.sqlite'),                      # Or path to database file if using sqlite3.
            # The following settings are not used with sqlite3:
            'USER': '',
            'PASSWORD': '',
            'HOST': '',                      # Empty for localhost through domain sockets or '127.0.0.1' for localhost through TCP.
            'PORT': '',                      # Set to empty string for default.
        }
}
ALLOWED_HOSTS = ['127.0.0.1', 'localhost']
TIME_ZONE = 'Europe/Vienna'
LANGUAGE_CODE = 'de'

ugettext = lambda s: s
LANGUAGES = [
    ('de', gettext('Deutsch')),
    ('en', gettext('English')),
]

SITE_ID = 1

USE_I18N = True
USE_L10N = True
USE_TZ = False
MEDIA_ROOT = os.path.join(PROJECT_PATH, "media").replace('\\','/')
MEDIA_URL = '/media/'
STATIC_ROOT = ''
STATIC_URL = '/static/'

STATICFILES_FINDERS = (
    'django.contrib.staticfiles.finders.FileSystemFinder',
    'django.contrib.staticfiles.finders.AppDirectoriesFinder',
)

SECRET_KEY = '**REMOVED**'

TEMPLATE_LOADERS = (
    'django.template.loaders.filesystem.Loader',
    'django.template.loaders.app_directories.Loader',
)

MIDDLEWARE_CLASSES = (
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.locale.LocaleMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'crequest.middleware.CrequestMiddleware',

    'debug_toolbar.middleware.DebugToolbarMiddleware',
)

ROOT_URLCONF = 'Roadrunners.urls'

WSGI_APPLICATION = 'Roadrunners.wsgi.application'

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'django.contrib.admin',
    'autoslug',
    'debug_toolbar',
    'easy_thumbnails',
    'crispy_forms',
    'VariousHelpers',
    'django_filters',
    'VerifiedDocuments',
    'VMS',
    'django_countries',
    'multiselectfield',
    'django_tables2', #// probleme mit 1.8
    'django_select2', #// probleme mit 1.8
    'mathfilters',
    'crequest',
    'Events',
    'Place',
    'data_importer', # // probleme mit 1.8
)

SESSION_SERIALIZER = 'django.contrib.sessions.serializers.JSONSerializer'

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'filters': {
        'require_debug_false': {
            '()': 'django.utils.log.RequireDebugFalse'
        }
    },
    'handlers': {
        'mail_admins': {
            'level': 'ERROR',
            'filters': ['require_debug_false'],
            'class': 'django.utils.log.AdminEmailHandler'
        }
    },
    'loggers': {
        'django.request': {
            'handlers': ['mail_admins'],
            'level': 'ERROR',
            'propagate': True,
        },
    }
}
TEMPLATE_CONTEXT_PROCESSORS=(
    "django.contrib.auth.context_processors.auth",
    "django.core.context_processors.debug",
    "django.core.context_processors.i18n",
    "django.core.context_processors.media",
    "django.core.context_processors.static",
    "django.core.context_processors.tz",
    "django.contrib.messages.context_processors.messages",
    "django.core.context_processors.request",
)

#TEMPLATE_DIRS = (os.path.join(os.path.dirname(__file__), '..', 'templates').replace('\\','/'),)
TEMPLATE_DIRS = (
    # Put strings here, like "/home/html/django_templates" or "C:/www/django/templates".
    # Always use forward slashes, even on Windows.
    # Don't forget to use absolute paths, not relative paths.
    os.path.join(PROJECT_PATH, "templates"),
    os.path.join(APPLICATION_PATH, "Place"),
    os.path.join(APPLICATION_PATH, "VerifiedDocuments"),
    os.path.join(APPLICATION_PATH, "Events"),
)

LOGIN_REDIRECT_URL = reverse_lazy('inside')
LOGIN_URL = reverse_lazy('login')
DEFAULT_FROM_EMAIL='******REMOVED******'

THUMBNAIL_PROCESSORS = (
    'easy_thumbnails.processors.colorspace',
    'easy_thumbnails.processors.autocrop',
    'easy_thumbnails.processors.scale_and_crop',
    'easy_thumbnails.processors.filters',
    'easy_thumbnails.processors.background',
)

CRISPY_TEMPLATE_PACK = 'bootstrap3'

INTERNAL_IPS = ('127.0.0.1',)

DEBUG_TOOLBAR_PANELS = (
   'debug_toolbar.panels.versions.VersionsPanel',
    'debug_toolbar.panels.timer.TimerPanel',
    'debug_toolbar.panels.settings.SettingsPanel',
    'debug_toolbar.panels.headers.HeadersPanel',
    'debug_toolbar.panels.request.RequestPanel',
    'debug_toolbar.panels.sql.SQLPanel',
    'debug_toolbar.panels.staticfiles.StaticFilesPanel',
    'debug_toolbar.panels.templates.TemplatesPanel',
    'debug_toolbar.panels.cache.CachePanel',
    'debug_toolbar.panels.signals.SignalsPanel',
    'debug_toolbar.panels.logging.LoggingPanel',
    'debug_toolbar.panels.redirects.RedirectsPanel',
)

def custom_show_toolbar(request):
    return True

DEBUG_TOOLBAR_CONFIG = {
    'INTERCEPT_REDIRECTS': False,
    'SHOW_TOOLBAR_CALLBACK': custom_show_toolbar,
    #'EXTRA_SIGNALS': ['myproject.signals.MySignal'],
    'HIDE_DJANGO_SQL': False,
    'TAG': 'div',
}


SELECT2_BOOTSTRAP = True
GENERATE_RANDOM_SELECT2_ID = True

TEST_RUNNER = 'django.test.runner.DiscoverRunner'

Answer 1

这实际上适合我，我得到：

<a href="?location=7">set</a>
<a href="">empty</a>

我怀疑你可能在模板中有一些缓存（块缓存）。如果没有，那么也许其他一些奇怪的事情正在弄乱你的要求。进行调试打印并查看它告诉您的内容以及它运行的次数：

def render(self, context):
    req = resolve_variable('request', context)
    params = req.GET.copy()
    print "----"
    print "\n".join("{}:{}".format(k, v) for k, v in params.items())
    print "----"