要在 base.html (Django) 中使用的上下文变量

Question

I need a certain context variable in my base.html. This is to contain a set of usernames, eg [name1, name2, name3, name4,] . If a logged in user's username is part of this list, I give said user certain preferential treatment and show something in the navbar.

To achieve this, I wrote a template tag :

from django import template
from django.db import models
from django.contrib.auth.models import User

register = template.Library()

VIPS = [name1, name2, name3, name4,]

@register.simple_tag
def verified(user):
    return VIPS

register.simple_tag(verified)

And then in base.html , I added {% load verified %} at the top, and then:

{% if user.username in verified %}
<!-- do something -->
{% endif %}

This isn't working. What am I doing wrong? I suspect I've written my template tag incorrectly, but I've tried several, more complex approaches (in vain), at least this simpler one made logical sense to me.

My project's a legacy Django 1.5 project with Python 2.7 .

Answer 1

You don't need the register.simple_tag(verified) line, as the @register decorator is already doing that.

However, you might consider a different approach to avoid additional processing in the template, assuming your user is coming from request.user ...

@regsiter.assignment_tag(takes_context=True)
def check_user_is_verified(context):
    user = context['request'].user
    return user and user in vips

Then in your template:

{% check_user_is_verified as is_verified %}
{% if is_verified %}
    {# whatever #}
{% endif %}

By leveraging an assignment tag, you can check if the user is verified once, and leverage the context variable you assign instead of having to perform the same list processing each time.

Another alternative is to use a cached property on a custom User object, or a "Profile" model that is linked to your User model via a OneToOneField.

from django.utils.functional import cached_property

class Profile(models.Model):
    user = models.OneToOneField(User)

    @cached_property
    def is_verified(self):
        # get the list of vips here
        return self.user in vips

If your list of vips changes, just clear the cache key, which you could do via a signal or a Celery task, etc:

del profile_instance.is_verified

Now you have a very efficient property you can check anywhere in your code. My preference tends to be fat models, skinny views and dumb templates.