ruby on rails - How do I store an instance variable across multiple actions in a controller?

Question

Say I want to store some variable in my controller. I want to initialize it in one action, increment it in another, and read it in yet another. Just declaring this variable with @foo doesn't work because @foo dies after the action that created it is rendered.
I do not want this variable to be stored in a model.

Is there a way to preserve this variable besides storing it in a session?
It seems like I've run into this simple problem a few times, and I want to know the best way to go about solving it.

Answer 1

Not really. Each call to a controller action is stateless. Nothing is available after the controller action finishes. A new controller instance is created for each request, and then discarded at the end of the request.

If you don't want to store it in the session, or database model, you don't have many options if you're wanting that variable to be specific to a particular session.

If it is global across all sessions, you could put it in a @@class_variable rather than an @instance_variable, but that can get messy once you start having multiple Rails processes (each which will have their own copy of it), or if you're running in threadsafe mode, you can end up with nasty concurrency bugs.

I guess you could look at something like memcached, but you'd still need to key that to some user_id or other session marker (unless it's global)