@classmethod
def create(cls, *args, **kwargs):
    """
        check there each image only has one relationship with product, comment or users
        """
    product_img = cls.product_img
    comment_img = cls.comment_img
    user_img = cls.user_img
    if not cls.onlyonebelongs(product_img, comment_img, user_img):
        raise ValueError('it only allows one belongs entity for saving')
    super().create(*args, **kwargs)
