Automatically add more items if an item exists in template - django

Question

I have an app that passes "book" object to the template from my view.
I want to automatically add more items to the template context if "book" is being passed. I don't want to do it for every view that passes "book".
e.g. if "book" exists, add "other_books_user_read" in relation to "books" to the template.
I was trying to do this using middleware but I cannot figure out how to check the context if "book" exists.

Answer 1

You can make a template tag that does this behavior, or you could put a method on your book model that you can access in the template.
Here's the simplest one to explain:
class Book(Model):
def other_books_users_read(self):
return Book.objects.filter(...)
{{ book.other_books_users_read }}
Template tag: It's your responsibility to figure out how a custom template tag works, but essentially the code would be...
#register.assignment_tag
def get_other_books_users_read(book):
return Book.objects.filter(...) # logic here to get the books you need.
{% get_other_books_users_read book as other_books_users_read %}
{% for book in other_books_users_read %}
...
Now, if you truly want it in the context, and one line of code (and a dot) is too much work, you can set up a middleware that injects content into the context.
https://docs.djangoproject.com/en/dev/topics/http/middleware/?from=olddocs#process-template-response
class MyMiddleware(object):
def process_template_response(self, request, response):
if 'book' in response.context_data:
response.context_data['other_books'] = Book.objects.filter(...)
return response
But IMO that's a silly way to use a template context middleware since you literally have access to a book object in your template.