foreign keys - Django - ForeignKey issue. How many DB accesses? -

foreign keys - Django - ForeignKey issue. How many DB accesses? -

i using django , model this.

class city(models.model): name = models.charfield(max_length=255, primary_key=true) url = models.urlfield() class paper(models.model): city = models.foreignkey(city) name = models.charfield(max_length=255) cost = models.integerfield() class article(models.model): paper = models.foreignkey(paper) name = models.charfield(max_length=255)

i trying city object, several paper objects , several article objects filtering through city name , cost of paper.

to search through city table can this:

cities = city.objects.get(pk='toronto')

to paper objects:

papers = paper.objects.filter(city=cities, cost < 5)

or combine two:

papers = cities.paper_set.filter(city=cities, cost < 5)

(will more efficient?)

the problem find efficient way articles above 'papers'.

i can't utilize papers.article_set since papers queryset. , if seek utilize loop making queries 1 time per paper object, right?

just reference city table has 1000 columns, there 1-1000 paper objects per city, , around 10 article objects per paper object.

any help appreciated.

thank you.

edit: assuming have cities queryset (above), there way article objects in single query?

articles = article.objects.all(paper__city__name='toronto', paper__price__lt=5)

django foreign-keys django-database