variables and state across forms and actions

I’d be grateful for pointers to or discussion of how and when Rails sets variables in forms and controllers. Here is the immediate problem:

I have a form, call it Form A, which modifies the state of an existing object and records that in the database. It sometimes wants a new object, so there’s a link to create a new one. That link goes to the usual form to create a new object of the appropriate kind. I’d like it to create the object, and then return to Form A – not the usual page shown after creation of the relevant object outside of this process.

I’ve been trying to pass the information in params. I can get params[:redirect] set to something when it comes time to render the form for creation of the new object. But I can’t seem to get it to persist long enough to be recognised by the controller that actually does the work, and which could then redirect to either the usual page or the unusual one.

Help? Please? As I’ve said, a general discussion of how to preserve little bits of state across pages would be really helpful to me. I know that I could use session variables, but it seems a big hammer for a little problem – or is that just the only hammer there is?

John Browning