Ошибка при создании нового экземпляра в модели

class Spisok_worker(models.Model):
 
    family = models.CharField(max_length=64, verbose_name='фамилия')
    name = models.CharField(max_length=64, verbose_name='имя')
    patronymic = models.CharField(max_length=64, verbose_name='отчество')

class Dostup_resurs(models.Model):
    smz = models.ForeignKey(Spisok_worker, on_delete=models.DO_NOTHING, verbose_name='проверяемый')
    date_pismo = models.DateField(verbose_name='Дата вложения шаблонов доступов')

def link(request, idsmz):    
    if request.method == 'POST':
        smz_dostup = Dostup_resurs()       
        smz = Spisok_worker.objects.get(pk=idsmz)
        smz_dostup.smz = smz        
        smz_dostup.save()

obj = Dostup_resurs.objects.get(pk=1)
print(obj.family)  # error
print(obj.smz.family)  # ok

smz_dostup = Dostup_resurs() 
smz_dostup.save()

smz_dostup = Dostup_resurs()
smz = Spisok_worker.objects.get(pk=1)
smz_dostup.smz = smz

proekt = models.FileField(upload_to=get_path, verbose_name='Проект')

smz_dostup.proekt = request.FILES['proekt']

smz_dostup.proekt = get_path(smz, request.FILES['proekt'])