如何在Rails配置中进行字符串插值？

Question

I am using the rails config gem to feed external urls into my application. I would like to do parameter interpolation in the following manner:

settings.yml

url: 'http://www.example.com/#{self.param}'

then in model.rb:

def get_path
    magic(Settings.url) #some magic procedure or function here
end

When I call get path I would like to have the fully interpolated url. Is there some "magic" function or method that would allow me to do that with railsconfig ? I would prefer something safer than passing the string into an eval call.

Answer 1

Assuming you want self.param interpreted at runtime when get_path is invoked, you could use ERB to parse the result. For example:

require 'erb'

def get_path(url, param)
  bar = "1"
  ERB.new(url).result(binding)
end

url = "http://www.example.com/<%= param %>?bar=<%= bar %>"
param = "foo"
puts get_path(url, param)

Would yield:

http://www.example.com/foo?bar=1

Answer 2

I ended up using the following method:

settings.yml:

url: 'http://www.example.com/%{param}'

model.rb:

def get_path
    Settings.url % {param: self.param}
end

which properly returns the current value of param interpolated into the string when model#get_path is called.