I solved this using a separate attribute in model:
class ModelFoo(Base):
__tablename__ = 'foo'
id = Column("id", Integer, primary_key=True, autoincrement=True)
os = Column(String, nullable=False)
platform = Column(String)
search_cols = ["os", "value"]
for k, v in list(Base._decl_class_registry.items()):
if (hasattr(v, "search_cols")):
cols = [getattr(v, val) for val in v.search_cols]
query = sess.query(*cols)
solr.add(query.all())