How to discard ActiveRecord's association cache

You know that ActiveRecord caches associations so they are not loaded twice for the same object. You also know that you can reload an association to make Rails load its data from the database again.

user.posts.reload
# discards cache and reloads and returns user.posts right away
# => [...]

If you want to discard the cache but not query the database (only the next time the association is accessed), you can use reset:

user.posts.reset
# discards cache, but does not load anything yet
user.posts
# SQL query happens to load new state
# => [...]

Note that reset returns the association/scope.

Hence, the above will not seem to work on the Rails console, just because the return value is inspected and thus resolved right away.
Try it like this:

user.posts.reset; nil
# no query
user.posts
# query, and returns results

Tip

You can also reload or reset plain scopes ("relations") that are not also associations.