Accessing instance variables within a Sinatra application - ruby

Question

This question has been rewritten because the way I originally wrote it was unclear.
How do I take the values within #form_params and pass them to get '/show_results'?
class MyApp < Sinatra::Base
configure :development do
register Sinatra::Reloader
end
get '/' do
erb :index
end
post '/form_handler' do
#form_params = params
redirect to("/show_results/?#{#form_params}")
end
get '/show_results' do
erb :display_result
end
end
index.erb
<form method="POST" action="/form_handler">
...
<input type="hidden" name="first" value="John">
<input type="hidden" name="middle" value="Q">
<input type="hidden" name="last" value="Public">
...
</form>
params (result)
{first => "John", middle => "Q", last => "Public"}

Answer 1

the #form_params is a hash in your code. sth like that:
{"first" => "John", "middle" => "Q", "last" => "Public"}.
actually it's a string but can be converted into hash.
when you apend it to the redirect url, it becomes,
/show_results?{"first" => "John", "middle" => "Q", "last" => "Public"}
and it is different from your expectation. as i guess you want something like that 0
/show_results?first=john&middle=Q ...
what you should do is,
take params and parse it. maybe sinatra has a built in method for this (better look documentation) but this can aslo easily be done with plain ruby.
post '/form_handler' do
redirect_url = '/show_results'
params.each { |k,v| redirect_url += "?#{k}=#{v}" }
#don't worry about above line, the rest of ?-s will be converted into &
redirect to(redirect_url)
end
apart from all these, why are you sending post request then redirect it to a get block?
if you submit your form with get, it will automatically will be parsed to
url?k1=v1&k2=v2 ..
i mean this.
index.erb
<form method="get" action="/form_handler">
<input type="text" name="first" value="John">
<input type="text" name="middle" value="Q">
<input type="text" name="last" value="Public">
<input type="submit" name="ok">
</form>
main file.
get '/' do
erb :index
end
get '/form_handler' do
erb :display_result
end
then in your display_result file, or inside get block, you can easily access the params[:first], params[:middle] and use them.

Answer 2

The params object is per-request. When you redirect, unless you explicitly pass them with the url they will be lost. By the way, you can use sessions, which passes data as a cookie but can be configured to use a database instead.
Here's an option if you require 'active_support/all'
redirect to("/show_name?#{my_hash.to_param}"):
In ActiveSupport (bundled with Rails, not Sinatra) the Hash#to_param method works like this:
hash = { a: 1, b: 2 }
hash.to_param
# => "a=1&b=2"
If you have learned about the components of a URL, you will know that query params can be passed after the ? in a url, which is how "/show_name?#{my_hash.to_param}" works.
It's nice that this method also works with hash and array params, which use a special syntax in the url, i.e. /path?my_list[]=1&my_list[]=2 makes param[:my_list] == ['1','2'].
Except that in some circumstances the & [ ] characters need to be escaped (replaced with special character sequences).
puts ({a: 1, b: [1,2]}.to_param)
# => a=1B%5D=1&b%5B%5D=2
URI.unescape CGI.unescape({a: 1, b: [1,2,3]}.to_param)
# => "a=1&b[]=1&b[]=2&b[]=3"