With following piece of code, what I want to achieve is that if patient is added in a appointment_ids then it should automatically get assigned/computed in respective doctor_id and vice versa means if doctor_id gets changed or set to False then it automatically gets deleted from appointment_ids. 

class DoctorAppointments(models.Model):
    _name = 'doctor.appointments'
    _description = 'Doctor's Appointments Info'
    doc_name = fields.Char('Doctor Name')
    appointment_ids = fields.Many2many('patient.patient')

class Patients(models.Model):
    _name = 'patient.patient'
    _description = 'Patient's Info'
    patient_name = fields.Char('Patient Name')
    doctor_id = fields.Many2one('patient.appointments', string='Patient Appointment')