Creating Template Links for Pagination in Generic CBV - django

Question

I'm just starting with Django so I have a lot of questions. I've built a Mixin to create the paginator template links for "next page" and previous page in a GCBV (ListView):
class PageLinksMixin:
page_kwarg = 'page'
def _page_urls(self, page_number):
return "?{pkw}={n}".format(pkw=self.page_kwarg, n=page_number)
def previous_page(self, page):
if page.has_previous():
return self._page_urls(page.previous_page_number())
return None
def next_page(self, page):
if page.has_next():
return self._page_urls(page.next_page_number())
return None
def get_context_data(self, **kwargs):
context = super().get_context_data(**kwargs)
page = context.get('page_obj')
if page is not None:
context.update({'previous_page_url': self.previous_page(page),
'next_page_url': self.next_page(page)})
return context
Everything seems to work. But I can simply not see where some of the inputs for functions were created. Especially "page", "page_number".
With a CBV it would be necessary to declare:
page = paginator.page(page_number)
But in the GCBV this is apparently unnecessary which means the attribute is created somewhere and later inherited.
For the ListView there is a function def paginate_queryset but in there page is only declared in a local scope not a global scope. Can somebody explain this to me? I'm really confused and trying to figure this out for a while now.
This is the View:
class TagList(PageLinksMixin, ListView):
template_name = 'organizer/tag_list.html'
paginate_by = 5
model = Tag

Answer 1

The Django generic ListView has a paginator object, which is added to the context through self.get_context_data(). Here's the Django source code:
def get_context_data(self, **kwargs):
"""
Get the context for this view.
"""
queryset = kwargs.pop('object_list', self.object_list)
page_size = self.get_paginate_by(queryset)
context_object_name = self.get_context_object_name(queryset)
if page_size:
paginator, page, queryset, is_paginated = self.paginate_queryset(queryset, page_size)
context = {
'paginator': paginator,
'page_obj': page,
'is_paginated': is_paginated,
'object_list': queryset
}
else:
context = {
'paginator': None,
'page_obj': None,
'is_paginated': False,
'object_list': queryset
}
if context_object_name is not None:
context[context_object_name] = queryset
context.update(kwargs)
return super(MultipleObjectMixin, self).get_context_data(**context)
In your mixin, you first call super().get_context_data(), which populates the context with the paginator and a page object, which you set to page:
page = context.get('page_obj')
Finally you call self.previous_page(page) to fetch the actual URL and add it to the context. Nothing magic.
You could also have fetched the page_number from the kwargs and the page from the paginator instance but since it's already done for you, the page_obj in the context is the easiest way.