Use correct foreign key of belongs_to associations

lib/assignable_values/active_record/restriction/belongs_to_association.rb

@@ -10,7 +10,12 @@ def association_class
         end
 
         def association_id_method
-          "#{property}_id"
+          association = model.reflect_on_association(property)
+          if association.respond_to?(:foreign_key)
+            association.foreign_key # Rails >= 3.1
+          else
+            association.primary_key_name # Rails 2 + 3.0
+          end
         end
 
         def error_property

lib/assignable_values/version.rb

@@ -1,3 +1,3 @@
 module AssignableValues
-  VERSION = '0.8.0'
+  VERSION = '0.8.1'
 end

spec/rails-2.3/Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ../..
   specs:
-    assignable_values (0.7.2)
+    assignable_values (0.8.1)
       activerecord
 
 GEM

spec/rails-3.0/Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ../..
   specs:
-    assignable_values (0.7.2)
+    assignable_values (0.8.1)
       activerecord
 
 GEM

spec/rails-3.2/Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: ../..
   specs:
-    assignable_values (0.7.2)
+    assignable_values (0.8.1)
       activerecord
 
 GEM

spec/shared/assignable_values/active_record_spec.rb

@@ -186,6 +186,18 @@
         error.should == I18n.t('errors.messages.inclusion')
       end
 
+      it 'uses the defined foreign key of the association' do
+        klass = Song.disposable_copy do
+          belongs_to :creator, :foreign_key => 'artist_id', :class_name => 'Artist'
+
+          assignable_values_for :creator do
+            []
+          end
+        end
+
+        klass.new(:creator => Artist.new).should have(1).error_on(:artist_id)
+      end
+
       it 'should allow a nil association if the :allow_blank option is set' do
         klass = Song.disposable_copy do
           assignable_values_for :artist, :allow_blank => true do