getting the flash hash to persist through redirects

Question

My basic use case is do some processing, set flash[:notice], and then redirect to a new page. From what I can tell, redirects reset the flash tag (please correct me if I'm wrong). Is there a way to gain persistence? Using sessions isn't an option, and I have hacked around the problem using cookies, but I think there's got to be a better way.

Answer 1

The flash hash persists for exactly one redirect or render. So you should be fine with the default settings.

If you need to keep the flash hash for another request/redirect, you can call flash.keep.

flash.keep # keep the entire flash hash around for an extra request. flash.keep(:notice) # keep just flash[:notice] for an extra request. 

Answer 2

Something to be aware of in at least Rails v3.2.1 is that the flash will persist through a redirect if its not referenced at all through at least 1 redirect and load the same view after. This is a pseudo code of my recent experience:

def some_action  (code that may set a flag to redirect 1 time)  redirect_to action_path if(redirect_flag) .... end 

Running this would result in the flash[:message] being present regardless of the redirect.

def some_action logger.debug("Flash[:message] #{flash[:message]}")  (code that may set a flag to redirect 1 time) redirect_to action_path if(redirect_flag) .... end 

During debugging with the logger referencing flash[] it would only show up when the redirect didn't happen. I could see this being problematic if you added a reference to flash before a redirect and lost it down the line for no apparent reason.

See ruby docs here (Instance protected method: Use at the bottom)