1 files changed, 14 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 55edb57206..3a741ba600 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -25,6 +25,11 @@ module ActiveRecord
 
         Array(options[:scope]).each do |scope_item|
           scope_value = record.send(scope_item)
+          reflection = record.class.reflect_on_association(scope_item)
+          if reflection
+            scope_value = record.send(reflection.foreign_key)
+            scope_item = reflection.foreign_key
+          end
           relation = relation.and(table[scope_item].eq(scope_value))
         end
 
@@ -51,7 +56,15 @@ module ActiveRecord
       end
 
       def build_relation(klass, table, attribute, value) #:nodoc:
-        column = klass.columns_hash[attribute.to_s]
+        reflection = klass.reflect_on_association(attribute)
+        column = nil
+        if(reflection)
+          column = klass.columns_hash[reflection.foreign_key]
+          attribute = reflection.foreign_key
+          value = value.attributes[reflection.primary_key_column.name]
+        else
+          column = klass.columns_hash[attribute.to_s]
+        end
         value = column.limit ? value.to_s[0, column.limit] : value.to_s if !value.nil? && column.text?
 
         if !options[:case_sensitive] && value && column.text?