将 editable 设置为 False 并将 default 设置为您的默认值.

Set editable to False and default to your default value.

http://docs.djangoproject.com/en/stable/ref/models/fields/#editable

b = models.CharField(max_length=7, default='0000000', editable=False)

此外，您的 id 字段是不必要的.Django 会自动添加.

Also, your id field is unnecessary. Django will add it automatically.