1 files changed, 13 insertions, 1 deletions
diff --git a/app/models/simple_interface.rb b/app/models/simple_interface.rb
index 3d5027bf1..5f022719a 100644
--- a/app/models/simple_interface.rb
+++ b/app/models/simple_interface.rb
@@ -167,6 +167,13 @@ class SimpleInterface < ActiveRecord::Base
       @scope = opts[:scope]
     end
 
+    def on_relation relation_name
+      @scope ||= []
+      @scope.push relation_name
+      yield
+      @scope.pop
+    end
+
     def duplicate
       self.class.new @import_name, self.options
     end
@@ -211,7 +218,8 @@ class SimpleInterface < ActiveRecord::Base
     end
 
     def add_column name, opts={}
-      @columns.push Column.new({name: name.to_s}.update(opts))
+      @scope ||= []
+      @columns.push Column.new({name: name.to_s, scope: @scope.dup}.update(opts))
     end
 
     def add_value attribute, value
@@ -262,6 +270,10 @@ class SimpleInterface < ActiveRecord::Base
         !!@options[:required]
       end
 
+      def scope
+        @options[:scope] || []
+      end
+
       def [](key)
         @options[key]
       end