In SqlAlchemy, how to ignore m2m relationship attributes when merge?
You'd better fix your code to avoid setting role.users for the item you are going to merge. But there is another way - setting cascade='none' for this relation. Then you lose an ability to save relationship from Role side, you'll have to save User with roles attribute set.
There is a m2m relation in my models,  User and Role.   
I want to merge a role, but i DO NOT want this merge has any effect on user and role relation-ship.  Unfortunately, for some complicate reason, role.users if not empty.  
I tried to set role.users = None, but SA complains None is not a list.
At this moment, I use sqlalchemy.orm.attributes.del_attribute, but I don't know if it's provided for this purpose.