My first RubyMotion application is rapidly nearing completion. As it involves user preferences that have to be stored both locally and remotely, I was investigating the available Rails gems for user preferences and really didn’t like what was presently out there. I don’t really have time to maintain another gem, but maybe someone else has run into this problem and wants a quick and easy solution for creating user preferences. If so, then this code’s for you.

Setting Up Preferences

You need a preference model. It should look like this:

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class Preference < ActiveRecord::Base
  belongs_to :user

  validates_uniqueness_of :name, :scope => :user_id

  attr_accessible :name, :value
end

I used this migration to create it:

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class CreatePreferences < ActiveRecord::Migration
  def change
    create_table :preferences do |t|
      t.string :name, :value
      t.integer :user_id
      t.timestamps
    end
  end
end

You might note that the value of all preferences, regardless of if they’re supposed to be Boolean or datetime, is a string. Keep this in mind when you have to query this field later. (That is, if you want to search for all preferences where the value is true, you’ll want to search for “1”. And similarly, doing user.preferences.first.true? will always return true, as any string value is true. So, coder beware!)

Using Them

Ideally, this is what we want the user model to look like.

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class User < ActiveRecord::Base
  include Preferences

  preference :chime, false
  preference :name, "Josh"
  preference :awesome, true

  ...
end

Simple but straightforward: we include the module and then define each preference, with its name first and default value second. Ideally we don’t want to save default values to the database, since that would just make a lot of unnecessary records.

The Preferences Module

So let’s make that happen in that include Preferences line! This is the real heart of the preferences engine.

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module Preferences
  extend ActiveSupport::Concern

  included do
    has_many :preferences
    @@preferences = {}
  end

  module ClassMethods
    def preference(name, default)
      preferences = self.class_variable_get(:'@@preferences')
      preferences[name] = default
      self.class_variable_set(:'@@preferences', preferences)
    end
  end

  def read_preference(name)
    if p = self.preferences.where(:name => name).first
      return p
    end
    return self.preferences.new(:name => name, :value => @@preferences[name]) if @@preferences.has_key?(name)
    nil
  end

  def write_preference(name, value)
    p = self.preferences.find_or_create_by_name(name)
    p.update_attribute(:value, value)
  end

  def method_missing(method, *args)
    if @@preferences.keys.any?{|k| method =~ /#{k}/}
      if method =~ /=/
        self.write_preference(method.gsub('=', ''), *args)
      else
        self.read_preference(method)
      end
    else
      super
    end
  end
end

This is really pretty simple. Upon inclusion it tells the model that it’s a part of that it has_many :preferences and sets up a class variable hash to store preferences and their defaults. When you declare preference :chime, true it records that in the class variable, and then all instances will respond to either user.chime = true or user.write_preference(:chime, true). You can read values with user.chime or user.read_preference(:chime). If a value isn’t written in the database, it returns the default value instead.

This probably has a level or two of refactoring that could happen around it. Maybe when I have time I will turn it into a more sensible gem, but until then, if anyone needs quick and dirty preferences… here you go.