Validate that the rating falls between the min and max values.

def save(self, *args, **kwargs):
        """
        Validate that the rating falls between the min and max values.
        """
        valid = map(str, settings.RATINGS_RANGE)
        if str(self.value) not in valid:
            raise ValueError("Invalid rating. %s is not in %s" % (self.value,
                ", ".join(valid)))
        super(Rating, self).save(*args, **kwargs)