When providing related or suggested info to the user in a website, it’s a common practice to obtain a random set of items. To do this in django the “usual” way is:
Book.objects.all().order_by('?')[:10]
The above code, sorts all books in a random order and then picks the first 10 objects. This approach is not really efficient en MySQL. Since the “ORDER BY ?” clause is really expensive. So, a good way to obtain random elemets (actually a random slice) is the following:
import random
count = Book.objects.all().count()
slice = random.random() * (count - 10)
Book.objects.all()[slice: slice+10]
The above code selects a random position for starting a slice (the next items are going to be consecutive). So it’s not really random.
Another approach is to get the random ids from Python:
from random import sample
count = Book.objecs.all().count()
rand_ids = sample(xrange(1, count), 10)
Book.objects.filter(id__in=rand_ids)
This last solution works fine for consecutive ids, where there are no missing elements. But you can always re call it until you have all the items you want.
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