替换redirect_to request.referer中的GET参数

Question

I'm trying to Replace GET params in:

redirect_to request.referer

My request.referer already contains one parameter:

http://www.foo.com/bar?par=10

When i try:

redirect_to request.referer, :par => 5

it doesn't work. It redirects to referer but doesn't change :par from 10 to 5. When i do redirect to url_path, eg

redirect_to root_path, :par => 5

This works ok, redirects to:

http://www.foo.com/?par=5

So my question is how to replace params in request.referer URI. Additional question is whether should I use request.referer or :back ?

Thanks

Answer 1

The problem is that redirect_to ultimately just takes a string, ie the url. If you were to do something like

redirect_to edit_foo_path(@foo, :bar => "qux")

then you're using a path helper to generate that string. ie, edit_foo_path(:bar => "qux") is the helper and it will be converted to "/foo/123/edit?bar=qux" which is just a "dumb" string. If you were working with the helper you can switch the params around but with the string it's already finished, if you know what i mean.

request.referer is a string as well, so what you'll need to do is to break it down into its constituent parts, modify those parts as required, and then reassemble it into a string again. The parts in question are protocol, host, path & params. You don't need to change the protocol, host or path in this case so you can keep them the same. params will be most easily manipulated when converted to a hash. Rails has various url-processing functions which you can use here, so there's probably a few different ways of doing this. I would do this like follows, which probably isn't the most efficient.

url = URL(request.referer)
#you could get this via a regex but i'm doing it "formally" with the Url object
host_and_path = "#{url.scheme}://#{url.host}#{url.path}"
params = CGI.parse(url.query)
#now you've got params as a hash you can do what you want to it.
params["par"] = 5
new_url = "#{host_and_path}?#{params.to_param}"
redirect_to new_url

like i say there's probably more efficient (in terms of lines of code, there's no issues with it speed-wise) ways to do this, but it's useful to see the step-by-step approach anyway i guess.