stderr

Tested with Rails 4.0

Just a quick note since I could not find this information anywhere. Making sure a has_many association is reloaded on next access is easy. Just call the reset method provided by the collection proxy:

class Post
  has_many :comments
end

post.comments.reset
post.comments # fetches comments from database

But how to accomplish the same for has_one associations?

class Post
  has_one :last_comment, -> { order 'created_at' }, class_name: "Comment"
end

Calling post.last_comment just returns a comment (or nil). Of course, you can pass true as the force_reload parameter:

post.last_comment(true) # fetches comment from database

But what if there is no need to reload the association now, only next time it is used? Turns out the underlying association object can be accessed via the associations method:

post.associations(:last_comment).reset

Now the cache is cleared and the next call to post.last_comment will fetch the record from the database.