Django - Selecting related set : how many times does it hit the database?

I took this sample code here : Django ORM: Selecting related set

polls = Poll.objects.filter(category='foo')
choices = Choice.objects.filter(poll__in=polls)
开发者_运维问答

My question is very simple : do you hit twice the database when you finally use the queryset choices ?

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It will be one query, but containing an inner SELECT; if you want to do some debugging on that, you could either use the marvellous django-debug-toolbar, or do something like print str(choices.query) which will output the raw sql of your query!