Deleting an Object from Collection in SQLAlchemy

I am storing a bunch of patent data in a MySQL database and interacting with it via SQLAlchemy. I have a collection inside the Patent class that represents the list of assignees (the companies that were assigned the patent): ``` assignees = relationship('Company', secondary=patent_company_table, backref='patents') ``` I am processing some of the objects stored in the database and for a Patent object `p`, I want to delete some assignee `a` (a Company object) from `p`'s assignee list. Based off of http://docs.sqlalchemy.org/en/latest/orm/session.html#deleting-from-collections , it seems that calling `s.delete(a)` will actually delete the Company object `a`. I simply want to remove assignee `a` from the list of assignees for `p` (i.e. remove a row in the patent_company_table), NOT actually delete the Company object, because `a` might be in another Patent object's list of assignees. I tried creating a new list `new_assignees` that only includes the assignees from `p` besides `a` and then called: ``` p.assignees = new_assignees s.add(p) ``` This unfortunately does not actually mark `p` as dirty, so I assume it would not affect the database. Do you have any suggestions for how to remove an object from the collection, deleting the row in the patent_company_table as opposed to deleting the object from the Company table? Thank you. UPDATE Here is a snippet of the code: ``` assignees = patent.assignees for assignee in assignees: if assignee in duplicate_company_to_default: patent.assignees.remove(assignee) default_company = duplicate_company_to_default[assignee] if default_company not in assignees: added_patent_count += 1 patent.assignees.append(default_company) ``` After looping through all of the patents, `added_patent_count = 983672` but there are no objects in `session.dirty()`. Do I need to add manually to the session after modifying via `append` or `remove`?