DRY Up Your Url Helpers

This tutorial shows you how to simplify url generation in combination with RESTful resources by extending the url_for helper. This approach will also work with nested routes and other helpers like form_tag and link_to.

One of the concepts of REST is: each resource has its own unique URI. We will enhance the url_for helper to generate this unique URI for an arbitrary record.

Example Models

First we need a simple example. We have 2 models: User and Article. For our url generation to work we have to add following code to our models:

class User
  has_many :articles
  def to_params
    {:id => permalink}
  end
end
class Article
  belongs_to :user
  def to_params
    {:user_id => user.permalink, :id => permalink}
  end
end

This is necessary for nested routes to play nicely with our url generation code. We are now able to find the parameters for each record to generate an unique URL.

Pretty URLs

In a previous post I demonstrated the use of meaningful urls. We are going now the same way.

Users are identified by an URL like:

/users/matthias-georgi

Each user may write articles, which are located at:

/users/matthias-georgi/articles

If I want to write a new article, I will use this URL:

/users/matthias-georgi/articles/new

Editing an existing article would end up on this URL:

/users/matthias-georgi/articles/my-first-post;edit

For nested resources to get working you define in config/routes.rb:

map.resources :users do |user|
  user.resources :articles
end

The traditional way to generate urls is to call the resource helpers:

article_url(article.user, article)

This is redundant, as the article already knows its user.

The Resource Helper

Add following module into your lib folder and include the module in both your application controller and application helper. The most important bit is the url_for method. It will automatically generate the right url for your resource.

module ResourceHelper
  def plural_class_name(record)
    singular_class_name(record).pluralize
  end
  def singular_class_name(record)
    record.class.name.underscore.tr('/', '_')
  end
  def params_for(record)
    if record.respond_to?(:to_params)
      record.to_params
    else
      {:id => record.to_param}
    end
  end
  def collection_url(collection, record, options)
    if record
      params = params_for(record)
      params["#{singular_class_name(record)}_id".to_sym] = params.delete(:id)
      url_for options.merge(params).merge(:controller => collection)
    else
      url_for options.merge(:controller => collection)
    end
  end
  def member_url(record, options)
    url_for options.merge(params_for(record)).merge(:controller => plural_class_name(record))
  end
  def url_for(*args)
    if [String, Hash].any? {|type| args.first.is_a? type }
      super(*args)
    else
      if args[0].is_a?(Symbol)
        collection_url(args[0], args[1], :action => 'index')
      else
        member_url(args.first, :action => 'show')
      end
    end
  end
  def new_url_for(collection, record=nil)
    collection_url(collection, record, :action => 'new')
  end
  def edit_url_for(record)
    member_url(record, :action => 'edit')
  end
  def path_for(*args)
    if args[0].is_a?(Symbol)
      collection_url(args[0], args[1], :action => 'index', :only_path => true)
    else
      member_url(args.first, :action => 'show', :only_path => true)
    end
  end
  def new_path_for(collection, record=nil)
    collection_url(collection, record, :action => 'new', :only_path => true)
  end
  def edit_path_for(record)
    member_url(record, :action => 'edit', :only_path => true)
  end
end

Usage

So how can you use this stuff actually?

It is pretty easy: just pass the record instead of the url hash and the unique url will be generated automatically.

The url of a collection is treated differently. You have to pass the name of the collection, which is the controller name. For nested resources you have to pass additionally the record, the collection is belonging to.

Some examples:

new_path_for(:users)          # => '/users/new'
path_for(user)                # => '/users/harald'
edit_path_for(user)           # => '/users/harald;edit'
path_for(:articles, user)     # => '/users/harald/articles'
new_path_for(:articles, user) # => '/users/harald/articles/new'
path_for(article)             # => '/users/harald/articles/article-1'
edit_path_for(article)        # => '/users/harald/articles/article-1;edit'
# This works for helpers like url_for, form_tag or link_to. 
link_to article.title, article
form_tag :articles
form_tag article, :method => 'put'

If anybody is interested I will release this stuff as plugin. I think other helpers could benefit as well as you can pass your records around and each helper may generate the appropriate url.

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