Django, topic model with subtopics

i wanted to create a topic model. this model would have a foreign key, non required, to 开发者_C百科the topic above it for example:

iphone has a foreign key to apple

but what do i do if i want apple to be linked to all of its sub elements

apple to iPhone apple to mac

i know that there are many to many fields, but how exactly would you apply them to this situation

furthermore mac or iPhone might even have more sub elements

You probably want to look at the documentation for related_name. Basically Django does this for you. For example:

class Topic(models.Model):
    master_topic = models.ForeignKey('self',
                     null=True,
                     blank=True,
                     related_name="sub_topics")

Then access this code:

apple = Topic.objects.filter(tag='Apple')
sub_topics = apple.sub_topics.all() ## Gets all sub_topics.