A Django template tag for the current active page

An important part of a usable web site is a well-designed navigation bar. Something that any navigation bar should have is an indication of where the user is. Common practices for this include using a bold face for the link, a different color or adding a small icon next to the current section link. To do that, you could include your navigation code in every page and use an “active” class name on the a element to distinguish it from the other links.

<div id="navigation">
    <a href="/">Home</a>
    <a href="/services/">Services</a>
    <a class="active" href="/contact/">Contact</a>
</div>

Writing this in every template quickly becomes a pain in the neck. With Django, an easy solution would be to move this section to a different file, _nav.html for instance, and include it in every page. Another, even better way, would be to make sure that every template extends a base template (a very common practice with Django) and to add the navigation to that base template.

We face a little problem however: how do we know which page we’re on? If you use the render_to_response shortcut, you can give an extra keyword argument, context_instance. If you use the RequestContext class, you can pass more data to the template (the generic views use RequestContext by default, so you don’t have to worry about them.) Here’s how to do it:

## settings.py
TEMPLATE_CONTEXT_PROCESSORS = (
    'django.core.context_processors.request',
)

## views.py
from django.template import ContextRequest

def home(request):
    return render_to_request('home.html', {}, context_instance=RequestContext(request))

You can now use the request template variable in home.html and its parent templates, which should include your base template. The HttpRequest object has an attribute, path, which contains the current URL (starting after the host name). We can now add the active class to the link for the current section:

<div id="navigation">
    <a class="{% ifequal request.path "/" %}active{% endifequal %}" href="/">Home</a>
    <a class="{% ifequal request.path "/services/" %}active{% endifequal %}" href="/services/">Services</a>
    <a class="{% ifequal request.path "/contact/" %}active{% endifequal %}" href="/contact/">Contact</a>
</div>

This code has two problems: (1) it’s really ugly (it’s probably all that should matter to make you want to rework this code), and (2) imagine that there are subsections under the services section, /services/web-hosting/, /services/tech-support/, etc. When you’re under one of those subsections, the link to the services section will not be highlighted. We’ll fix that by using a custom template tag that will check if request.path begins with a given string.

## tags.py
@register.simple_tag
def active(request, pattern):
    if request.path.startswith(pattern):
        return 'active'
    return ''

<!-- navigation -->

{% load tags %}
<div id="navigation">
    <a class="{% active request "/" %}" href="/">Home</a>
    <a class="{% active request "/services/" %}" href="/services/">Services</a>
    <a class="{% active request "/contact/" %}" href="/contact/">Contact</a>
</div>

Ah, the code is much nicer and now if we go to /services/web-hosting/, the services link will still be highlighted. Another link will be highlighted unfortunately: the home link will ALWAYS be highlighted, because every path begins with a slash. Let’s change the implementation of the active tag slightly to use regular expressions and we’ll also change the calls to {% active %}

## tags.py
@register.simple_tag
def active(request, pattern):
    import re
    if re.search(pattern, request.path):
        return 'active'
    return ''

<!-- navigation -->

{% load tags %}
<div id="navigation">
    <a class="{% active request "^/$" %}" href="/">Home</a>
    <a class="{% active request "^/services/" %}" href="/services/">Services</a>
    <a class="{% active request "^/contact/" %}" href="/contact/">Contact</a>
</div>

Nice! Now it’s how we want it. Home will be highlighted only when we’re viewing the / URL, the subsections still work and the code is still pretty cute.

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