Person security profile by assignment

Summary

Person security profile by assignment

Content

Hi,

we need to setup a custom person security profile based on a query that let logged in user see only assignments who belongs to a certain Business Unit. For example, if an employee has two assignments, on two different business units, the logged in user will be able to see only the assignment of the business unit set in his Area of responsibility. 

Is there a way to do this or person security profiles works only by person_id? (Example: if I'm able to see an employee, I'll see all his assignments).