Template used by multiple apps requires a specific variable-CodePudding

When one uses a template, used by various apps, that requires a specific variable

<a href="{% url 'blog:blog-detail' user_blog %}">My blog</a>

we want to ensure that the template will always be aware of the variable user_blog. Also, we don't want to hammer the logic in every view.

In such cases, the question popping up is usually within the lines of "How to make a variable available to all templates?" and so we are redirected to Template context processors.

Since what we want is dependent on a user instance, we wouldn't be able to use a context processor for something like this

user_blog = self.request.user.blog
return {'user_blog': user_blog}

because, as noted by Willem Van Onsem

A contextprocessor only passes extra variables to the template render engine, so it returns a dictionary, and does not take any parameters (except for the request).

What do we then do in such cases?

CodePudding user response：

In such case you don't really need to use Template Context Processors.

You can simply do the following in the template

<a href="{% url 'blog:blog-detail' request.user.blog %}">>My blog</a>

Needless to say you ought to check if request.user.blog exists or not.

CodePudding user response：

A context processor actually had access to the request object:

# context_processors.py
def getBlog(request):
    return { 'user_blog': request.user.blog }

But! request.user is already available from inside the template, so you don't need a context processor.

But if request.user -> blog isn't a direct connection you could do something like:

Note: More-so just showing it's possible

# context_processors.py
def getBlog(request):
    from myproject.thing.models import Blog
    return { 'user_blog': Blog.objects.filter(user=request.user).first() }

The better route (so you're not always hitting the DB on every request) is to add a cache:

# context_processors.py
def getBlog(request):

    from django.core.cache import cache

    cachedname = 'UserBlog:{0}'.format(request.user.username)
    cachedData = cache.get(cachedname)

    if cachedData:
        # in cache (yay!)
        return { 'user_blog': cachedData }

    else:
        # not in cache (boo!) 

        from myproject.thing.models import Blog
        user_blog = Blog.objects.filter(user=request.user).first()

        cache.set(cachedname, user_blog, 600) # 10 minute cache

        return { 'user_blog': user_blog }