如何在 django 中没有循环的情况下获取 foreighkey 的 foreighkey？

Question

这是一个 Django 项目，我正在尝试创建一个心愿单（多对多无济于事，因为我需要在心愿单中获取该心愿单的 DateTime）。

class Client(models.Model):
    name = models.CharField(max_length=100)
    user = models.ForeignKey(User, on_delete=models.CASCADE)


class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField()

class WishItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    client = models.ForeignKey(Client, related_name="wishlist", on_delete=models.CASCADE)
    added_at = models.DateTimeField(auto_now_add=True)

我能做的只有这个：

wishlist = Client.objects.wishlist.select_related('product').all()
wish_products = [item.product for item in wishlist]

但我需要这样的东西，没有循环但有一个 SQL 查询和单行

wishlist = Client.objects.wishlist.product.all()

当我尝试运行这段代码时，出现错误 AttributeError: 'RelatedManager' object has no attribute 'product'

Answer 1

多对多关系可以解决您可以向 WishItem 添加额外字段的问题 class 您可以试试这个：

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField()

 class Client(models.Model):
    name = models.CharField(max_length=100)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    WishProducts = models.ManyToManyField(Product,through='WishItem')


class WishItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    client = models.ForeignKey(Client, on_delete=models.CASCADE)
    added_at = models.DateTimeField(auto_now_add=True)

Answer 2

您可以 .filter(…) ^[Django-doc] and then .order_by(…) ^[Django-doc] 使用：

Product.objects.filter(<b>wishitem__client__user=<i>my_user</i></b>).order_by(<b>'wishitem__added_at'</b>)

您可以将 ManyToManyField 与您的 WishItem:

class Client(models.Model):
    # …
    wishlist = models.<strong>ManyToManyField(</strong>
        'Product',
        <strong>through='WishItem'</strong>
    <strong>)</strong>


class Product(models.Model):
    # …
    pass

class WishItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    client = models.ForeignKey(Client, related_name='wishitems', on_delete=models.CASCADE)
    added_at = models.DateTimeField(auto_now_add=True)

那么你可以查询：

Product.objects.filter(<b>client__user=<i>my_user</i></b>).order_by(<b>'wishitem__added_at'</b>)

这也将使查询 Client 的 .wishlist 更加方便，Product 的 .client_set 是管理 Client 有 Product 在心愿单上。

Note: It is normally better to make use of the settings.AUTH_USER_MODEL ^[Django-doc] to refer to the user model, than to use the User model ^[Django-doc] directly. For more information you can see the referencing the User model section of the documentation.

如何在 django 中没有循环的情况下获取 foreighkey 的 foreighkey？

how do I get foreighkey of foreighkey without a loop in django?

django

django-models

python-3.x