The default Volt::ModelController proxies any missing methods to its model. Sometimes you need to store additional data reactively in the controller outside of the model. (Though often you may want to consider making another controller). In this case, you can add a reactive_accessor. These behave just like attr_accessor except that the values assigned and returned are tracked reactively.
module Main
class Contacts < Volt::ModelController
reactive_accessor :query
end
end
Now, from the view, we can bind to query while also changing in and out the model. When query is accessed it tracks that it was accessed and will rerun any computations when it changes.