How to get validated in DJANGO?

Question

Django

class Course(models.Model):
    objects = CourseManager()

    class Meta:
        ordering = ('ccy',)
        verbose_name = _('course.model.verbose_name')
        verbose_name_plural = _('course.model.verbose_name_plural')
        unique_together = ('ccy', 'base_ccy')


    def __str__(self):
        return str(self.ccy.code) + '/' + str(self.base_ccy.code)

    # первая валюта
    ccy = models.ForeignKey(Currency, verbose_name=_('course.model.ccy'), related_name="ccy")

    # вторая валюта
    base_ccy = models.ForeignKey(Currency, verbose_name=_('course.model.base_ccy'), related_name="base_ccy")

    # покупаем
    buy = models.DecimalField(verbose_name=_('course.model.buy'), max_digits=20, decimal_places=10, default=0)

    # продаем
    sale = models.DecimalField(verbose_name=_('course.model.buy'), max_digits=20, decimal_places=10, default=0)

    # время последнего обновления
    updated_at = models.DateTimeField(auto_now=True)

    def clean(self):
        if Course.objects.get(ccy=self.base_ccy, base_ccy=self.ccy):
            raise ValidationError('Уже есть обратное направление!')

I have the above model. The model has one uniqueness condition when saving by two fields unique_together = ('ccy', 'base_ccy') and additionally, a check on the reverse direction of fields has been added in the clean method. I ran into a problem when saving Course matching query does not exist correctly, and when it is incorrect, the clean method works. Tell me how to get around this problem?

Answer 1

If the only information you need is whether such an entry exists in the database, then there is a special method for this: exists
djbook.ru/rel1.7/ref/models/querysets.html#django....