SQLAlchemy: Hybrid Expression With Relationship (on Parent)

Similar to question SQLAlchemy: Hybrid expression with relationship but I would like to know what is the best method to implement hybrid expresions on the parent. The adapted examp

Solution 1:

from sqlalchemy import select, func

    @n_teachers.expression
    def n_teachers(self):
        return select([func.count(Teacher.id)]).where(Teacher.id_school == self.id).as_scalar()