I am not sure whether it is correct topic I choose.
I want to check, whether have the fixture in the employee to set department. so he/she cannot see other department sales or purchase.
such as, John and lucy are the purchaser of Raw Material department . Andy and gleen are purchaser for Export department.
So, whether have the rule to prevent each department to see other department records.
Add a field to specify from which department a purchase or a sale belongs.
Once all this steps are done you should create a record rule for sales and purchases with a domain that restricts the department to the one of the current employee.