Fix uniqueness validation to correctly work with STI

lib/dm-validations/validators/uniqueness_validator.rb

@@ -42,8 +42,9 @@ def valid?(target)
           opts[subject] = target.__send__(subject)
         }
 
+        property = target.model.properties[field_name]
         resource = DataMapper.repository(target.repository.name) do
-          target.model.first(opts)
+          property.model.first(opts)
         end
 
         return true if resource.nil?

spec/fixtures/corporate_world.rb

@@ -18,6 +18,7 @@ class Department
 
         property :id, Serial
         property :name, String, :unique_index => true
+        property :type, Discriminator
 
         validates_uniqueness_of :name
       end
@@ -34,6 +35,9 @@ class User
         validates_uniqueness_of :user_name, :when => :signing_up_for_department_account,   :scope => [:department]
         validates_uniqueness_of :user_name, :when => :signing_up_for_organization_account, :scope => [:organisation]
       end
+
+      # For STI uniqueness testing
+      class BigDepartment < Department; end
     end
   end
 end

spec/integration/uniqueness_validator/uniqueness_validator_spec.rb

@@ -26,6 +26,14 @@
 
       it_should_behave_like "invalid model"
     end
+
+    describe "with duplicate name in a child class" do
+      before do
+        @model = DataMapper::Validations::Fixtures::BigDepartment.new(:name => "HR")
+      end
+
+      it_should_behave_like "invalid model"
+    end
   end
 
   describe 'DataMapper::Validations::Fixtures::Organisation' do