Simple active record class to store in database some application settings adjustable by users

application_setting.rb

class ApplicationSetting < ActiveRecord::Base
  belongs_to :setting_type
  validates_presence_of :code, :name, :value, :setting_type
  validates_uniqueness_of :code
  attr_accessible :code, :name, :value, :setting_type, :setting_type_id
  
  class << self
    #for usage like ApplicationSetting["some_setting_code"]
    def [] key
      find_by_code(key).try :value
    end
  end
  
  def value
    #setting type could be decimal, integer, string
    case setting_type.name
      when "decimal" then BigDecimal( read_attribute(:value).to_s )
      when "integer" then read_attribute(:value).to_i
      else read_attribute(:value)
    end
  end
end

application_setting_test.rb

require 'test_helper'

class ApplicationSettingTest < ActiveSupport::TestCase
  test "should return value of a setting when setting's coe is passed in []" do
    assert_equal ApplicationSetting["SUFFICIENT_USER_LEVEL"], 8 #this setting is seeded in our application
  end
  
  test "should return nil if no setting found" do
    assert_equal ApplicationSetting["lala"], nil
  end
  
  test "should convert value string to interger, if setting_type is integer" do
    as = ApplicationSetting.new(:code => "code", :name => "name", :setting_type => SettingType.find_by_name("integer"), :value => "5")
    
    assert_equal as.value.class, Fixnum
    assert_equal as.value, 5
  end
  
  test "should convert value string to BigDecimal, if setting_type is decimal" do
    as = ApplicationSetting.new(:code => "code", :name => "name", :setting_type => SettingType.find_by_name("decimal"), :value => "5.78")
    
    assert_equal as.value.class, BigDecimal
    assert_equal as.value, 5.78
  end
  
  test "should return plain value if setting_type is other than decimal or integer" do
    as = ApplicationSetting.new(:code => "code", :name => "name", :setting_type => SettingType.find_by_name("string"), :value => "5.78")
    
    assert_equal as.value.class, String
    assert_equal as.value, "5.78"
  end
  
  test "should return nil if value attribute is nil" do
    as = ApplicationSetting.new(:code => "code", :name => "name", :setting_type => SettingType.find_by_name("string"), :value => nil)
    
    assert_equal as.value.class, NilClass
    assert_equal as.value, nil
  end
  
  
end

migration_create_application_setting.rb

class CreateApplicationSettings < ActiveRecord::Migration
  def change
    create_table :application_settings do |t|
      t.integer :setting_type_id
      t.string :code
      t.string :value
      t.string :name

      t.timestamps
    end
  end
end

migration_create_setting_types.rb

class CreateSettingTypes < ActiveRecord::Migration
  def change
    create_table :setting_types do |t|
      t.string :name

      t.timestamps
    end
  end
end

migration_indeces_for_application_settings.rb

class SettingsFkIndeces < ActiveRecord::Migration
  def up
    add_index :application_settings, :code, :unique => true
    add_index :application_settings, :setting_type_id
  end

  def down
    remove_index :application_settings, :column_name =>:code
    remove_index :application_settings, :column_name =>:setting_type_id
  end
end

setting_type.rb

class SettingType < ActiveRecord::Base
  has_many :application_settings
end