class Physician(models.Model):
    user = models.OneToOneField(User)
    patients = models.ManyToManyField(Patient, through='MedicalCase',
                                      related_name='physicians')
    hospital = models.ForeignKey(Hospital, related_name='physicians')
    collaborator = models.ForeignKey(Collaborator, related_name='physicians')
    phone_number = PhoneNumberField()
    access_code = models.CharField(max_length=20)
    educational_materials = models.FileField(
        upload_to='user_files/educational_materials')
    preview_file = models.FileField(upload_to='user_files/preview_files')
    speciality = models.CharField(max_length=50)