Add model_mapper and model_table attributes to base importer class

rattail/db/newimporting/importers.py

@@ -72,6 +72,22 @@ class Importer(object):
         """
         return self.model_class.__name__
 
+    @property
+    def model_mapper(self):
+        """
+        This should return the SQLAlchemy mapper for the model class.
+        """
+        return orm.class_mapper(self.model_class)
+
+    @property
+    def model_table(self):
+        """
+        Returns the underlying table used by the primary local data model class.
+        """
+        tables = self.model_mapper.tables
+        assert len(tables) == 1
+        return tables[0]
+
     @property
     def simple_fields(self):
         """
@@ -80,8 +96,7 @@ class Importer(object):
         only applies to the local / target side, it has no effect on the
         upstream / foreign side.
         """
-        mapper = orm.class_mapper(self.model_class)
-        return list(mapper.columns.keys())
+        return list(self.model_mapper.columns.keys())
 
     @property
     def supported_fields(self):