python - Django: Link a field of one model to a field of another -

i'm working through tango django book , have decided add of own functionality have issue.

i have 2 models, category , page

class category(models.model):     name = models.charfield(max_length=128, unique=true)     views = models.integerfield(default=0)     likes = models.integerfield(default=0)     slug = models.slugfield(unique=true)  class page(models.model):     category = models.foreignkey(category)     title = models.charfield(max_length=128)     url = models.urlfield()     views = models.integerfield(default=0) 

now i'm trying make category "views" field sum of views of of pages within category

in test database population script doing way:

cats = {"python": {"pages": python_pages,                    "views": sum(page["views"] page in python_pages),                    },         "django": {"pages": django_pages,                    "views": sum(page["views"] page in django_pages),                    },         "other frameworks": {"pages": other_pages,                              "views": sum(page["views"] page in other_pages),                              }         } 

this works populating database, how make category "views" updates whenever page "views" field changed?

for example if 2 different pages in same category's "views" go one, category's "views" go two?

i add category class instead of using views field:

def get_views(self):     views=0     page in pages_set:         views+=page.views     return views