Just Read The Directions
(Because sometimes that helps.)
Articles on programming by Phil Darnowsky.

Announcing has_named_bootstraps (June 26, 2010)

Most nontrivial Web apps will require some amount of bootstrap data to be present in the database. Classic examples are lists of countries, US states, or postal codes. In my work at Children's Hospital Boston, we frequently deal with lists of clinics or diagnoses. If you're using role based access control (RBAC), you'll need different roles to be preloaded.

You might write part of the logic for RBAC like this:

  class AdminController < ApplicationController
  before_filter :require_admin_user

  ...

  private

  def require_admin_user
    admin_role = Role.find_by_name 'admin'
    unless current_user.roles.include?(admin_role)
      flash.now[:error] = "You're not authorized to do that."
      redirect_to peon_path
    end
  end

But what's wrong with doing it this way?

You end up repeating Role.find_by_name(...) a million times. Of course, in practice, you'd write methods with names like is_admin?, is_moderator?, is_regular_user?. But these all have the same structure and vary only in what role they're concerned with, indicating that we have a chance to DRY things up.
You're hardcoding strings. One of the first things I learned in programming, and quite likely one of the first things you learned, is that this always leads to trouble eventually. A role's name will change, or you'll type "administrator" where you meant "admin", or any of innumerable variations.
You'll often want to refer to values bootstrapped in this way all together, perhaps in a <select> or a listing on an index page. Of course you can always find(:all) and grab every instance of that model, but I find that you often want to treat the bootstrapped values differently from other instances that might get created.

Dan Chak, in his book Enterprise Rails, suggests that you create a constant to refer to this kind of data. I don't agree with everything in this book, but I do believe that this particular advice is on the money. So our example from above might turn into:

  def require_admin_user
  unless current_user.roles.include?(Role::ADMIN)
    flash.now[:error] = "You're not authorized to do that."
    redirect_to peon_path
  end
end

This could still be DRYer, but it's definitely a step in the right direction.

Having defined a few gazillion of these constants in some of my code, I wrote and recently open-sourced a gem called has_named_bootstraps (with source on GitHub) that automates defining these constants. There are plenty of options to play with, but the most basic case just looks like:

  class Department < ActiveRecord::Base
  has_named_bootstraps(
    :R_AND_D         => 'R&D',
    :MARKETING       => 'Marketing',
    :HANDSOME_DEVILS => 'Web Development'
  )
end

The constants R_AND_D, MARKETING, and HANDSOME_DEVILS are now all defined on Department.

Feedback, bug reports and pull requests are all most welcome. I'm eager to hear what you think.

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Just Read The Directions (Because sometimes that helps.) Articles on programming by Phil Darnowsky.

Announcing has_named_bootstraps (June 26, 2010)

Just Read The Directions
(Because sometimes that helps.)
Articles on programming by Phil Darnowsky.