Mongo Mapper Custom Type

gistfile1.rb

class Direction
  attr_reader :short, :long
  
  def self.to_mongo(value)
    case value.long
    when 'north'
      'n'
    when 'northeast'
      'ne'
    when 'east'
      'e'
    when 'southeast'
      'se'
    when 'south'
      's'
    when 'southwest'
      'sw'
    when 'west'
      'w'
    when 'northwest'
      'nw'
    when 'down'
      'd'
    when 'up'
      'u'
    when 'n', 'ne', 'e', 'se', 's', 'sw', 'w', 'nw', 'd', 'u'
      value
    else
      raise 'Invalid direction.'
    end
  end
  
  def self.from_mongo(value)
    value.is_a?(self) ? value : Direction.new(value)
  end
  
  def initialize(value)
    if value == 'north' or value == 'northeast' or value == 'east' or value == 'southeast' or value == 'south' or value == 'southwest' or value == 'west' or value == 'northwest' or value == 'up' or value == 'down'
      raise 'Invalid direction.  Use two-letter short-hand notation.'
    end
    
    case value
    when 'n'
      @short = value
      @long = 'north'
    when 'ne'
      @short = value
      @long  = 'northeast'
    when 'e'
      @short = value
      @long = 'east'
    when 'se'
      @short = value
      @long = 'southeast'
    when 's'
      @short = value
      @long = 'south'
    when 'sw'
      @short = value
      @long = 'southwest'
    when 'w'
      @short = value
      @long = 'west'
    when 'nw'
      @short = value
      @long = 'northwest'
    when 'u'
      @short = value
      @long = 'up'
    when 'd'
      @short = value
      @long = 'down'
    else
      raise 'Invalid direction.'
    end
  end
  
end

Depending on what your looking for, I think we could improve the below; however, hopefully it demonstrates an alternative.

class Direction
  include MongoMapper::Document
  key :direction, String, required: true
  validate :direction_is_abbreviated

  LEDGER = {
    'n' => 'north',
    'ne' => 'northeast',
    'e' => 'east',
    'se' => 'southeast',
    's' => 'south',
    'sw' => 'southwest',
    'w' => 'west',
    'nw' => 'northwest',
    'd' => 'down',
    'u' => 'up'
  }

  def long
    LEDGER[direction]
  end

  def short
    direction
  end

  private

  def direction_is_abbreviated
    case
    when LEDGER.has_value? direction
      self.direction = LEDGER.index(direction)
    when LEDGER.has_key? direction
      self.direction = direction
    else
     errors.add(:direction, "Invalid direction. Use one or two letter short-hand notation.")
    end
  end

end