marshmallow + SQLAlchemy

TeacherModel (SQLAlchemy)
    id = db.Column(db.Integer, primary_key=True)
    uuid = db.Column(db.String(32), nullable=False, unique=True)

StudentModel (SQLAlchemy)
    id = db.Column(db.Integer, primary_key=True)
    uuid = db.Column(db.String(32), nullable=False, unique=True)

    teacher_id = db.Column(db.Integer, db.ForeignKey("teachers.id"), nullable=False)
    teacher = db.relationship("TeacherModel")

StudentSchema (Marshmallow)
    model = StudentModel

    # Custom field
    teacher_uuid = fields.String()

class AddStudent(Resource):
    json = request.get_json()
    student = student_schema.load(student_json)

    # I can't get this to work:
    parent = student.teacher_uuid