ModelLoader Columns objects support in column loader

gino/loader.py

@@ -56,7 +56,7 @@ def __init__(self, model, *column_names, **extras):
         self.model = model
         self._distinct = None
         if column_names:
-            self.columns = [getattr(model, name) for name in column_names]
+            self.columns = self._column_loader(model, column_names)
         else:
             self.columns = model
         self.extras = dict((key, self.get(value))
@@ -123,11 +123,24 @@ def get_from(self):
 
     def load(self, *column_names, **extras):
         if column_names:
-            self.columns = [getattr(self.model, name) for name in column_names]
+            self.columns = self._column_loader(self.model, column_names)
+
         self.extras.update((key, self.get(value))
                            for key, value in extras.items())
         return self
 
+    @classmethod
+    def _column_loader(cls, model, column_names):
+        def column_formatter(column_name):
+            if isinstance(column_name, str):
+                return getattr(model, column_name)
+            elif isinstance(column_name, Column):
+                return column_name
+            else:
+                raise TypeError('Unknown column name {} type {}'.format(column_name, type(column_name)))
+
+        return [column_formatter(column_name) for column_name in column_names]
+
     def on(self, on_clause):
         self.on_clause = on_clause
         return self

tests/test_loader.py

@@ -48,6 +48,9 @@ async def test_model_load(user):
     assert u.id is None
     assert u.nickname == user.nickname
 
+    with pytest.raises(TypeError):
+        await User.query.gino.load(User.load(123)).first()
+
 
 async def test_216_model_load_passive_partial(user):
     u = await db.select([User.nickname]).gino.model(User).first()
@@ -144,6 +147,27 @@ def loader(row, context):
         assert u.team.parent.name == user.team.parent.name
 
 
+async def test_adjanency_list_on_nested_load(user):
+    subquery = db.select(User).alias()
+    base_query = subquery.outerjoin(Team).select()
+
+    query = base_query.execution_options(loader=(User.load('id')))
+    u = await query.gino.first()
+    # Because here arrives team_id, not user_id, and replaces it
+    assert u.id is None
+
+    query = base_query.execution_options(loader=(User.load(
+        *(map(subquery.corresponding_column, User)), team=Team)))
+    u = await query.gino.first()
+    assert u.id == user.id
+    assert u.realname == user.realname
+    assert u.nickname == user.nickname
+
+    assert isinstance(u.team, Team)
+    assert u.team.id == user.team.id
+    assert u.team.name == user.team.name
+
+
 async def test_adjacency_list_query_builder(user):
     group = Team.alias()
     u = await User.load(team=Team.load(parent=group.on(