Creating a Hierarchy View in Django - django

Question

I'm trying to create a hierarchy view in Django, but I'm struggling to make sense of how to use QuerySets effectively.
What I'm aiming for eventually is a html page that displays courses like this:
Main Course 1 --- Child Course 1
--- Child Course 2
Main Course 2 --- Child Course 3
--- Child Course 4
Each group of courses would be wrapped in a div and styled etc.
In my view.py file I have the following:
class HierarchyView(generic.ListView):
template_name = 'curriculum/hierarchy.html'
def get_queryset(self):
return Offering.objects.all()
def get_context_data(self, **kwargs):
context = super(HierarchyView, self).get_context_data(**kwargs)
context['main'] = self.get_queryset().filter(course_type='M')
context['sub'] = self.get_queryset().filter(parent_code__in=context['main'])
return context
The Offering model is set up so that parent_code is a self-referential foreign key (i.e. any course can be a child of any other), like this:
...
parent_code = models.ForeignKey(
'self',
null=True,
blank=True,
on_delete=models.SET_NULL)
...
And in my html template I have:
{% for mainoffering in main %}
<div>
<div>{{ mainoffering.course_name }}</div>
{% for offering in sub %}
<div>{{ offering.course_name }}</div>
{% endfor %}
</div>
{% endfor %}
What this results in, however, is that all child courses appear under all main courses, regardless of whether or not they are actually children of that course, which is obviously not what I'm after.
I'm still learning the ropes in Django, and I'm struggling to find anything that explains in plain English what I need to do. Please help!

Answer 1

I think you would need to change your template to match each of the child courses to their parent courses. Maybe something like:
{% for mainoffering in main %}
<div>
<div>{{ mainoffering.course_name }}</div>
{% for offering in sub %}
{% if offering.parent_code == mainoffering %}
<div>{{ offering.course_name }}</div>
{% endif %}
{% endfor %}
</div>
{% endfor %}

Answer 2

The context['sub'] will return all of them, without any grouping, ordering etc. You can do couple of things to get the desired behavior.
You can do a prefetch related.
from django.db.models import Prefetch
offerings = Offering.objects.filter(course_type='M').prefetch_related(
Prefetch(
"courses_subset",
queryset=Offering.objects.filter(parent_code__in=offerings),
to_attr="sub"
)
)
for o in offerings:
print o.sub
You can actually make this a method in your model and create a template tag (i'd most likely use this).
method in your Offering model
def get_child_courses(self):
child_courses = Offerings.objects.filter(parent_code=self.id)
return child_courses
template tag
#register.simple_tag
def get_child_courses(course):
return course.get_child_courses()
In your template:
{% for mainoffering in main %}
<div>
<div>{{ mainoffering.course_name }}</div>
{% for offering in mainoffering|get_child_course %}
<div>{{ offering.course_name }}</div>
{% endfor %}
</div>
{% endfor %}
You can group them in your template as suggested by accraze. I'd personally go for the second option