Django：用于多对多关系的自定义保存方法 [英] Django: Custom Save method for Many-to-Many relation

问题描述

我需要在多对多关系中设置自定义保存和删除方法。

I need to set custom save and delete methods on a Many-to-Many relation.

我尝试使用through属性指定一个模型，但是这个复杂的我的代码并介绍了一些问题。在多对多模型中，我不需要任何额外的字段，只需自定义保存和删除方法。

I tried specifying a model with the "through" attribute but this over-complicated my code and introduced some problems. I don't need any extra field on the Many-to-Many model, just custom save and delete methods.

是否可以在不指定通过属性？

Is it possible to accomplish this without specifying the "through" attribute?

这里是代码：

class Order(BaseDate):
    #lots of fields
    relateds = models.ManyToManyField('RelatedProduct', verbose_name=_('related products'), blank=True, related_name='order_relateds', through='OrderRelateds')
    # more fields
    total = CurrencyField(verbose_name=_('total'))

    def calculate_total(self):
        cleanses = self.cleanse.taxed_price() * self.quantity
        delivery = DELIVERY_PRICE if self.delivery == 'delivery' else 0
        relateds = 0
        for r in self.relateds.all():
            relateds = relateds + float(r.taxed_price())
        total = float(cleanses) + delivery + relateds
        return total

    def save(self, *args, **kwargs):
        self.total = '%.2f' % self.calculate_total()
        super(Order, self).save(*args, **kwargs)

class OrderRelateds(models.Model):
    order = models.ForeignKey(Order)
    relatedproduct = models.ForeignKey(RelatedProduct, verbose_name=_('related product'))

    class Meta:
        verbose_name = _('Related Product')
        verbose_name_plural = _('Products Related to this Order')

    def __unicode__(self):
        return self.relatedproduct.__unicode__()

    def save(self, *args, **kwargs):
        super(OrderRelateds, self).save(*args, **kwargs)
        self.order.save()

    def delete(self, *args, **kwargs):
        super(OrderRelateds, self).delete(*args, **kwargs)
        self.order.save()

我需要触发重新计算如果添加相关产品（许多项目）t的订单总价格t o或从订单中删除。

I need to trigger recalculation of total price of the order if any related product (many to many item) is added to or removed from an order.

编辑：这是解决我的问题的代码

from django.db.models.signals import m2m_changed
from django.dispatch import receiver

@receiver(m2m_changed, sender=Order.relateds.through)
def recalculate_total(sender, instance, action, **kwargs):
    """
    Automatically recalculate total price of an order when a related product is added or removed
    """
    if action == 'post_add':
        instance.save()
    if action == 'post_remove' or action == 'post_clear':
        instance.save()

推荐答案

您可以使用django的< a href =https://docs.djangoproject.com/en/dev/ref/signals/ =noreferrer> m2m_changed ，包含关系的模型的pre_save / post_save ， pre_delete / post_delete信号 ，并执行相关的逻辑 那里。

You could make use of django's m2m_changed, pre_save/post_save, pre_delete/post_delete signals on the Model containing the relation, and do the related logic there.

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