Question

I have a User model witch i have override the to_param method.

i made it like this:

class User < ActiveRecord::Base

  def to_param
    if self.id < 100
      if self.id < 10
        s = "00#{self.id}"
      else
        s = "0#{self.id}"
      end
    else
      s = "#{self.id}"
    end
    return "usr-#{s}"
  end

end

And on my controller:

user = User.find(params[:id])
@title = user.name

the problem is… i can`t get any users…

if i change the to_param method to: return "#{s}-usr" it simple ignores the -usr and search for the id without taking -usr

i already tried an after_save filter, but i could`n change an atribute on there.

how can i create an unique id to an user based on his id ?

Answer 1

Rails won’t do inverse transformation for you, you have to do it yourself. I think you can do it like that:

class User < ActiveRecord::Base

  # Returns formatted user id:
  #
  #   1    => 'usr-001'
  #   11   => 'usr-011'
  #   111  => 'usr-111'
  #   1111 => 'usr-1111'      
  #
  def to_param
    "usr-%03d" % id
  end 

  def self.from_param(param)
    # ruby strips leading zeros for us (e.g., '012'.to_i returns 12)
    # but we need to remove 'usr-' prefix first
    find(param[4..-1].to_i)
  end 

end

and then use it in wherever you need it:

user = User.from_param params[:id]

In addition, have a look at to_param docs. Description and examples clearly state that this method is used for generating urls, but developer is the one responsible for finding corresponding record by this parameter.

Regarding strings formatting you can find more info in docs for String#% method and Kernel#format method it uses.