move :preference to principal

This allows for eager loading preference. As the UserPreferences are pretty specific to users we don't want groups to actually receive a UserPreference, though. The methods added by has_one are therefore undefined on the Group model.

app/models/group.rb

@@ -44,6 +44,18 @@ class Group < Principal
   validate :uniqueness_of_groupname
   validates_length_of :groupname, maximum: 30
 
+  # HACK: We want to have the :preference association on the Principal to allow
+  # for eager loading preferences.
+  # However, the preferences are currently very user specific.  We therefore
+  # remove the methods added by
+  #   has_one :preference
+  # to avoid accidental assignment and usage of preferences on groups.
+  undef_method :preference,
+               :preference=,
+               :build_preference,
+               :create_preference,
+               :create_preference!
+
   def to_s
     lastname.to_s
   end

app/models/principal.rb

@@ -42,6 +42,10 @@ class Principal < ActiveRecord::Base
 
   self.table_name = "#{table_name_prefix}users#{table_name_suffix}"
 
+  has_one :preference,
+    dependent: :destroy,
+    class_name: 'UserPreference',
+    foreign_key: 'user_id'
   has_many :members, foreign_key: 'user_id', dependent: :destroy
   has_many :memberships, -> {
     includes(:project, :roles)

app/models/user.rb

@@ -93,7 +93,6 @@ class User < Principal
   }, class_name: 'UserPassword',
      dependent: :destroy,
      inverse_of: :user
-  has_one :preference, dependent: :destroy, class_name: 'UserPreference'
   has_one :rss_token, -> {
     where("action='feeds'")
   }, dependent: :destroy, class_name: 'Token'

spec/models/group_spec.rb

@@ -83,4 +83,17 @@ describe Group, type: :model do
       end
     end
   end
+
+  describe 'preference' do
+    %w{preference
+       preference=
+       build_preference
+       create_preference
+       create_preference!}.each do |method|
+
+      it "should not respond to #{method}" do
+        expect(group).to_not respond_to method
+      end
+    end
+  end
 end