[PATCH] ActiveRecord live scope #to_json fix. Prevents the CircularReferenceError error

Calling #to_json on a live ActiveRecord scope will always raise the following error:

ActiveSupport::JSON::Encoding::CircularReferenceError: object references itself

This is because entity that gets passed to the JSON encoder is the ActiveRecord::Relation instance instead of the loaded array of records.

Started noticing this error when working on a Rails 3.beta4 app and using the respond_with(@records) call on my controller without firing off the scope:

respond_to :html, :json

def index
  @users = User.most_recent
  respond_with(@users)
end

Patch overrides the #to_json method on ActiveRecord::Relation so that it makes sure the scope is loaded and the method is called on the @records collection.

Test is included that fails without the patch.