Merge pull request #20 from cbmi/issue-19

Add support for passing the originating model to ModelTree.add_select

modeltree/tree.py

@@ -932,8 +932,14 @@ def add_select(self, *fields, **kwargs):
 
         aliases = []
 
-        for field in fields:
-            queryset, alias = self.add_joins(field.model, queryset, **kwargs)
+        for pair in fields:
+            if isinstance(pair, (list, tuple)):
+                model, field = pair
+            else:
+                field = pair
+                model = field.model
+
+            queryset, alias = self.add_joins(model, queryset, **kwargs)
 
             col = (alias, field.column)