Allow only 3 rows to be added to a table for a specific value

Question

I have a question in hand where i need to restrict the number of projects assigned to a manager to only 3. The tables are:

Manager:
Manager_employee_id(PK)
M         


        

Answer 1

I would do the following:

1. Create one SP for both operation insert/update.
2. Check with IF not exists Project_manager_employee_id(FK) count < 3 then only proceed for insert/update. otherwise send Throw error.