Does Django cache related ForeignKey and ManyToManyField fields once they're accessed?

Question

Given the following model, does Django cache the related objects after the first time they're accessed?

class Post(models.Model):
    authors = models.ManyToManyField(User)
    category = models.ForeignKey(Category)

For example:

post = Post.objects.get(id=1)

# as i understand this hits the database
authors1 = post.authors.all()
# does this his the database again?
authors2 = post.authors.all()

# as i understand this hits the database
category1 = post.category
# does this hit the database again?
category2 = post.category

Note: currently working with Django 1.3, but it's good to know what's available in other versions.

Answer 1

In the first example the second query is cached. In the second case (I believe) they will both cause a DB hit unless you use select_related on the original query:

post = Post.objects.select_related('category').get(id=1)

EDIT

I'm wrong about the second example. If you use select_related in the original query, you won't hit the database at all again (The ForeignKey is cached immediately). If you don't use select_related, you will hit the DB on the first query but the second query will be cached.

From:

https://docs.djangoproject.com/en/dev/topics/db/queries/#one-to-many-relationships

Forward access to one-to-many relationships is cached the first time the related object is accessed. Subsequent accesses to the foreign key on the same object instance are cached.

Note that the select_related() QuerySet method recursively prepopulates the cache of all one-to-many relationships ahead of time.