詹戈：如何获取外键ID？

Question

我有2个模型如下class Product(models.Model):   product_name = models.CharField(max_length=100)   product_weight = models.CharField(max_length=30)class ProductImage(models.Model):   product = models.ForeignKey(Product, on_delete=models.DO_NOTHING)   image = models.ImageField(upload_to='/images/{product_id}/', blank=True)如何在产品图像模型中提取product_id？提前致谢。

Answer 1

您可以通过在字段名称中添加“_id”来获取Django中任何外键的“原始”值

obj = ProductImage.objects.get()
obj.product_id  # Will return the id of the related product

您也可以只关注关系，但如果尚未使用类似的东西缓存关系，这将执行另一个数据库查找select_related

obj.product.id

Answer 2

这是我到目前为止尝试并找到解决方案的方法。我发现实现的唯一选择是使用pre_save和post_save信号。以下是我如何实现解决方案。如果有人有不同的解决方案，请分享。谢谢。

from django.db.models.signals import post_save, pre_save

from django.dispatch import receiver

_UNSAVED_IMAGEFIELD = 'unsaved_imagefield'

def upload_path_handler(instance, filename):

    import os.path

    fn, ext = os.path.splitext(filename)

    return "images/{id}/{fname}".format(id=instance.product_id, 

    fname=filename)

class ProductImage(models.Model):

   product = models.ForeignKey(Product, on_delete=models.DO_NOTHING)

   image = models.ImageField(upload_to=upload_path_handler, blank=True)

@receiver(pre_save, sender=ProductImage)

def skip_saving_file(sender, instance, **kwargs):

    if not instance.pk and not hasattr(instance, _UNSAVED_IMAGEFIELD):

        setattr(instance, _UNSAVED_IMAGEFIELD, instance.image)

        instance.image = None

@receiver(post_save, sender=ProductImage)

def update_file_url(sender, instance, created, **kwargs):

    if created and hasattr(instance, _UNSAVED_IMAGEFIELD):

        instance.image = getattr(instance, _UNSAVED_IMAGEFIELD)

        instance.save()

Answer 3

只需在国外参考模型产品中添加str函数即可。

class Product(models.Model):

  product_name = models.CharField(max_length=100)

  product_weight = models.CharField(max_length=30)

  def __str__(self):

      return str(self.id)