Everyday Rails

Building Rails apps faster with Nifty Generators, part 2: nifty_config

By Aaron Sumner, May 27, 2010.

Continuing with my series on the Nifty Generators gem by Ryan Bates (see part 1 on nifty_layout), in this post I want to talk about a second feature this gem provides, called nifty_config. With nifty_config, you can quickly create a set of global variables for your application, dependent on the environment in which your Rails application is currently running.

To get started, generate a config file:

  $ script/generate nifty_config

This adds two files to your app: A configuration file called app_config.yml located inside config, and an initializer (to load the config file when your Rails app starts) in config/initializers.

    domain: localhost:3000

    domain: test.host

    domain: example.com

From there you can customize the default values created by the generator. For example, I use the Passenger preference pane for Mac OS X to manage multiple local development environments, instead of running script/server within my apps. The preference pane defaults to appname.local as its convention, so I use that as my local domain.

You can also add your own values to the YAML file. For me, the most useful addition is an e-mail address for mailers to use when sending e-mail. I might use a personal account during development, but a more official contact address once the app is in production. I sometimes also include a name value for each environment, mainly because there are times I’ll start on application development before I know what it’s going to be called–so I use some sort of code name during development, and want to have placeholders for the final name. This isn’t always a good practice, but it generally works for me. It’s no substitute for error-checking your views and your copy before deployment, though.

Here’s what a completed config.yml file might look like for me:

    name: My Great App Development
    domain: mygreatapp.local
    email: devaccount@mygreatapp.com

    name: My Great App Test
    domain: test.host
    email: devaccount@mygreatapp.com

    name: My Great App
    domain: mygreatapp.com
    email: help@mygreatapp.com

Don’t forget: The values in your app_config.yml file are loaded when your application starts, so you’ll need to restart your application after you first create the file or whenever you make changes to its values.

From there, it’s just a matter of calling up your values wherever they’re needed. All you need to do is refer to APP_CONFIG[:value] within your application’s code to use whatever you assigned to value in your config.yml file, for the environment in which your app is currently running. For example, given the above configuration file, APP_CONFIG[:email] would return devaccount@mygreatapp.com if I were running the code in development mode; it would return help@mygreatapp.com if I were in production.

So in a standard Rails view file, you might include your application’s name like

  <h1>Welcome to <%= APP_CONFIG[:name] %>!</h1>

Using Haml, I’d write the above like

  %h1= "Welcome to #{APP_CONFIG[:name]}!"

Or in a mailer model like

  def message(sent_at = Time.now)
    subject    "#{APP_CONFIG[:name]}: New message received"
    recipients @message.recipient.email
    from       APP_CONFIG[:email]
    sent_on    sent_at
    body       :greeting => 'Hi,'

Here’s a simple example of using APP_CONFIG values outside of view-type files. In this case, I wanted to limit the number of people who could create accounts while I was scaling up. I created a max_users value in my app_config.yml file, then called the below method with a before_filter call in the controller that created new user accounts.

  def room_for_user?
    if User.count >= APP_CONFIG[:max_users]
      flash[:error] = 'Sorry, we have all the users we can handle right now.'
      redirect_to root_path

That’s all for Nifty Generators’ nifty_config feature. These are my uses for it, but I recommend experimenting with it in your own apps. Next time I’ll close out my series on Nifty Generators with nifty_scaffold, the real meat of this very useful gem.

How am I doing? I’m still getting a feel for this blog and how to write for it. If you’re reading (thanks, by the way) I’d love to hear what you think of what I’ve written so far. Please leave a comment with any input you care to share.


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