Lets say I have two models connected by a OneToOne field like so:

class Post(models.Model):
    ...


class MagicalPost(models.Model):
    post = models.OneToOneField('Post')
    pony = models.TextField(max_length=100, help_text='This is where the MAGIC happens!')

I want to run a query over all MagicalPost objects but I only want to receive the Post instances.

I can use the select_related() option which will only create one database call:

magical_posts = MagicalPost.objects.select_related('post')
posts = []

for magical_post in magical_posts:
    posts.append(magical_post.post)

return posts

Or I could use two queries which syntactically is simpler:

posts_ids = MagicalPost.objects.values_list('post', flat=True)
posts = Post.objects.filter(id__in=posts_ids)
return posts