Django: Remove duplicate messages from storage

问题

I'm using messages to add flash messages to the template (just as you'd expect).

The problem I have is that if you double click a link to a page that generates a message then the message appears twice.

I am using the message to tell the user I have redirected them from where they were expecting to go. They don;t need the same message twice.

I understand the logic here but am wondering how I can remove duplicated messages.

click url
message generated, saved in storage
click url again before page renders
second message generated, saved in storage
response adds all messages from storage
renders with two messages

Ultimately I would like this to be a middleware so it can cover off all requests.

回答1:

Ran into the same problem and found another solution, using a custom MESSAGE_STORAGE:

from django.contrib.messages.storage.session import SessionStorage
from django.contrib.messages.storage.base import Message


class DedupMessageMixin(object):
    def __iter__(self):
        msgset = [tuple(m.__dict__.items())
                  for m in super(DedupMessageMixin, self).__iter__()]
        return iter([Message(**dict(m)) for m in set(msgset)])


class SessionDedupStorage(DedupMessageMixin, SessionStorage):
    pass


# in settings
MESSAGE_STORAGE = 'some.where.SessionDedupStorage'

This will work fine with code that would also play with messages directly, say in a view for example. Since it's a mixin, you can easily reuse it for other message storages.

Here is an alternative to avoid storing duplicates at all:

from django.contrib.messages.storage.session import SessionStorage
from itertools import chain


class DedupMessageMixin(object):
    def add(self, level, message, extra_tags):
        messages = chain(self._loaded_messages, self._queued_messages)
        for m in messages:
            if m.message == message:
                return
        return super(DedupMessageMixin, self).add(level, message, extra_tags)

回答2:

I had the same problem in middleware but preferred a little wrapper around the info call that I was using:

from django.contrib.messages import info
from django.contrib.messages import get_messages


def info_once_only(request, msg):
    """
    Just add the message once
    :param request:
    :param msg:
    :return:
    """
    if msg not in [m.message for m in get_messages(request)]:
        info(request, msg)


class PaymentsMiddleware(object):

    @staticmethod
    def process_request(request):
        """
        Put up a message letting a new user know that they are being dealt with.
        :param request:
        :return:
        """
        if hasattr(request, 'user'):
            user_profile = request.user.get_profile()
            if user_profile and user_profile.is_suspended:
                info_once_only(
                    request,
                    "Hi {username}, your account has been suspended, we'll be in touch shortly.".format(                           
                        username=request.user.username))
    return None

回答3:

Opted for a custom TEMPLATE_CONTEXT_PROCESSORS.

Replace the default messages context processor ('django.contrib.messages.context_processors.messages',) with a simple custom version:

from django.contrib.messages.api import get_messages


def messages(request):
    """Remove duplicate messages

    """
    messages = []
    unique_messages = []
    for m in get_messages(request):
        if m.message not in messages:
            messages.append(m.message)
            unique_messages.append(m)

    return {'messages': unique_messages}

回答4:

For those using Paul Whipp's suggestion.

def info_once_only(request, msg):
    if msg not in [m.message for m in get_messages(request)]:
        info(request, msg)

Note that iterating over get_messages(request) will mark each message as 'to be cleared', so the user won't see any messages except the one passed into info_once_only(request, msg).

You should set storage.used = False so that all the other messages aren't cleared.

def info_once_only(request, msg):
    storage = get_messages(request)
    if msg not in [m.message for m in storage]:
        info(request, msg)
    storage.used = False

See the corresponding section in the official documentation.

来源：https://stackoverflow.com/questions/23249807/django-remove-duplicate-messages-from-storage

标签

django

django-middleware

django-messages