SQL Server: How to implement 3-way relationship with cascades

This is the schema I'm working with: Here's the DBML to recreate in https://dbdiagram.io/d : Table University { ID integer [primary key] } Table Professor { ID integer [primary key] UniversityID integer [primary key, ref: > University.ID] } Table Class { ID integer [primary key] UniversityID integer [primary key, ref: > University.ID] ProfessorID integer [null] } Ref: Class.(ProfessorID, UniversityID) - Professor.(ID, UniversityID) My goal: - A University can have multiple Classes and Professors. - A Class can have one or no Professors. - Deleting a University deletes all of its Professors and Classes - **Deleting a Professor sets Class.ProfessorID to NULL** The last goal is causing us problems. SQL Server prevents adding another cascading foreign key constraint due to multiple cascade paths, and a trigger can't work because: 1) the delete query is rejected due to the foreign key constraint on Professor, so a FOR DELETE trigger will never run 2) SQL cannot create an INSTEAD OF DELETE because of the cascading relationship to the University How can I achieve this?