generalised sunniness into a variable for later reuse

app/models/planting.rb

@@ -2,8 +2,8 @@ class Planting < ActiveRecord::Base
   extend FriendlyId
   friendly_id :planting_slug, use: :slugged
 
-  attr_accessible :crop_id, :description, :garden_id, :planted_at, :quantity,
-    :planted_at_string
+  attr_accessible :crop_id, :description, :garden_id, :planted_at,
+    :quantity, :sunniness, :planted_at_string
 
   belongs_to :garden
   belongs_to :crop
@@ -13,8 +13,10 @@ class Planting < ActiveRecord::Base
     :to => :crop,
     :prefix => true
 
-  validates :sunniness, :inclusion => { :in => %w(sun semi-shade shade),
-        :message => "%{value} is not a valid sunniness value" }
+  SUNNINESS_VALUES = %w(sun semi-shade shade)
+  validates :sunniness, :inclusion => { :in => SUNNINESS_VALUES,
+        :message => "%{value} is not a valid sunniness value" },
+        :allow_nil => true
 
   def planting_slug
     "#{owner.login_name}-#{garden}-#{crop}".downcase.gsub(' ', '-')

spec/models/planting_spec.rb

@@ -43,7 +43,7 @@ describe Planting do
   end
 
   it 'all three valid sunniness values should work' do
-    ['sun', 'shade', 'semi-shade'].each do |s|
+    ['sun', 'shade', 'semi-shade', nil].each do |s|
       @planting = FactoryGirl.build(:planting, :sunniness => s)
       @planting.should be_valid
     end