Django, querying data when we have table hierarchy

Question

Let's consider that we have three tables in a hierarchical form:

Course 
    Topic 
        Sub-Topic 

or in code:

class Course(models.Model):
    name            = models.CharField(max_length = 100)

class Topic(models.Model):
    name            = models.CharField(max_length = 100)
    course          = models.ForeignKey('Course' , null = True , blank = True)

class SubTopic(models.Model):
    name            = models.CharField(max_length = 100)
    topic          = models.ForeignKey('Topic' , null = True , blank = True)

What I want is to get list of Courses, Topics and sub-topics to represent in a tree like Navigation system.

I know that select_related() can follow and discover ForeignKeys in any depth. How can I get use of the feature in my scenario ?

Answer 1

If you simply want to output to a template you can use _set e.g. if you passed a list of courses to your template.

{% for c in courses %}
    {{c.name}}
    {% for t in c.topic_set.all %}
       {{t.name}}
       {% for st in t.subtopic_set.all %}
           {{st.name}}
       {% endfor %}
    {% endfor %}
{% endfor %}