select_related()
Returns a QuerySet that will automatically “follow” foreign-key relationships, selecting that additional related-object data when it executes its query. This is a performance booster which results in (sometimes much) larger queries but means later use of foreign-key relationships won't require database queries.
The following examples illustrate the difference between plain lookups and select_related() lookups. Here's standard lookup:
# Hits the database.
e = Entry.objects.get(id=5)
# Hits the database again to get the related Blog object.
b = e.blog
And here's select_related lookup:
# Hits the database.
e = Entry.objects.select_related().get(id=5)
# Doesn't hit the database, because e.blog has been prepopulated
# in the previous query.
b = e.blog