SQLAlchemy array_agg问题

Question

我正在尝试sqlalchemy-ize以下查询：

select feat.*, array_remove(array_agg(fa), null) as assets, array_remove(array_agg(fs), null) as styles 
              from features as feat
              LEFT JOIN feature_assets fa on feat.id = fa.feature_id
              LEFT JOIN feature_styles fs on feat.id = fs.feature_id
              where project_id = :projectId
              group by feat.id

到目前为止，我抛出的错误是这样的：

sqlalchemy.exc.ArgumentError: Object <class 'FeatureStyle'> is not legal as a SQL literal value

这段代码：

 db_session.query(
                [
                    Feature,
                    func.array_remove(func.array_agg(FeatureStyle), None),
                    func.array_remove(func.array_agg(FeatureAsset), None)
                 ]
            ).outerjoin(FeatureAsset)\
            .outerjoin(FeatureStyle)\
            .filter(Feature.project_id == projectId)\
            .group_by(Feature.id)

原始SQL查询有效。有一些聪明的方法来修复该sqlalchemy查询吗？