Django Context Processors: Injecting Global Template Variables

Consider displaying a list of article categories or shopping cart counts in your site header. Passing categories = Category.objects.all() manually in every view function violates DRY. Django solves this with Context Processors.

Building a Custom Context Processor

Create a file named context_processors.py inside your core app:

# blog/context_processors.py
from django.core.cache import cache
from .models import Category

def site_wide_categories(request):
    """Injects cached navigation categories into every template context."""
    categories = cache.get('nav_categories')
    if categories is None:
        categories = list(Category.objects.all())
        cache.set('nav_categories', categories, 60 * 60) # Cache for 1 hour

    return {
        'all_categories': categories,
        'site_name': 'Veewom Programming',
        'support_email': 'support@veewom.com'
    }

def cart_counter(request):
    """Calculates total shopping cart quantity from session."""
    cart = request.session.get('cart', {})
    total_items = sum(cart.values()) if isinstance(cart, dict) else 0
    return {
        'cart_total_count': total_items,
        'is_dark_mode': request.session.get('theme_mode', 'light') == 'dark'
    }

Registering in settings.py

Add your processor path under TEMPLATES['OPTIONS']['context_processors']:

# mywebsite/settings.py
TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [BASE_DIR / 'templates'],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',

                # Custom Project Context Processors
                'blog.context_processors.site_wide_categories',
                'blog.context_processors.cart_counter',
            ],
        },
    },
]

Now, {{ all_categories }}, {{ site_name }}, {{ cart_total_count }}, and {{ support_email }} are available instantly inside any HTML template without modifying a single view!

Context Processor vs Custom Template Tag: When to Use Which?