Django ValueError：字段“id”需要一个数字但得到“S”

Question

下面是我的模型，用于查看错误发生的地方，尤其是 StockQuantity 模型中发生错误的地方，当我尝试过滤或使用 get 检索查询时，它显示的是预期数字但得到了“字符串值”

models.py

# Item
class Item(models.Model):
    title = models.CharField(max_length=100)
    price = models.FloatField()
    discount_price = models.FloatField(blank=True, null=True)
    category = models.ForeignKey(
        'Category', on_delete=models.CASCADE, null=True)
    label = models.CharField(choices=LABEL_CHOICES, max_length=1)
    slug = models.SlugField()
    description = models.TextField()
    # stock_quantity = models.IntegerField(blank=True, null=True)
    cover_image = models.ImageField(blank=True, null=True,
                                    upload_to=item_cover_upload_location, default='no-product-image.jpg')

    is_footwear = models.BooleanField(default=False)
    upload_date = models.DateTimeField(default=timezone.now)

# StockQuantity
class StockQuantity(models.Model):
    item = models.ForeignKey('Item', on_delete=models.CASCADE, null=True)
    color = models.ForeignKey(
        'ItemColor', on_delete=models.CASCADE)
    cloth_size = models.ForeignKey(
        'ClothSize', on_delete=models.CASCADE, blank=True, null=True)
    footwear_size = models.ForeignKey(
        'FootwearSize', on_delete=models.CASCADE, blank=True, null=True)
    stock_quantity = models.IntegerField(null=True, default=10)

#OrderItem
class OrderItem(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    item = models.ForeignKey(Item, on_delete=models.CASCADE)
    quantity = models.IntegerField(default=1)
    footwear_size = models.CharField(max_length=50, null=True)
    cloth_size = models.CharField(max_length=50, null=True)
    color = models.CharField(max_length=50, null=True)
    ordered = models.BooleanField(default=False)

#Order
class Order(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    ref_code = models.CharField(max_length=20, blank=True, null=True)
    items = models.ManyToManyField(OrderItem)
    start_date = models.DateTimeField(auto_now_add=True)
    ordered_date = models.DateTimeField()
    ordered = models.BooleanField(default=False)
    shipping_address = models.ForeignKey(
        'Address', related_name='shipping_address', on_delete=models.SET_NULL, blank=True, null=True)
    billing_address = models.ForeignKey(
        'Address', related_name='billing_address', on_delete=models.SET_NULL, blank=True, null=True)
    payment = models.ForeignKey(
        'Payment', on_delete=models.SET_NULL, blank=True, null=True)
    coupon = models.ForeignKey(
        'Coupon', on_delete=models.SET_NULL, blank=True, null=True)
    being_delivered = models.BooleanField(default=False)
    received = models.BooleanField(default=False)
    requested_refund = models.BooleanField(default=False)
    refund_status = models.BooleanField(default=False)

#Payment
class Payment(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL,
                             on_delete=models.SET_NULL, blank=True, null=True)
    paypal_transaction_id = models.CharField(max_length=50)
    amount = models.FloatField()
    timestamp = models.DateTimeField(default=timezone.now)

# ItemColor
class ItemColor(models.Model):
    item_color = models.CharField(
        max_length=25, null=True, blank=True)
    item = models.ForeignKey('Item', on_delete=models.CASCADE, null=True)

    def __str__(self):
        return self.item_color

# ClothSize
class ClothSize(models.Model):
    cloth_size = models.CharField(
        max_length=25, null=True, blank=True)
    item = models.ForeignKey('Item', on_delete=models.CASCADE, null=True)

    def __str__(self):
        return self.cloth_size

# FootwearSize
class FootwearSize(models.Model):
    footwear_size = models.CharField(
        max_length=25, null=True, blank=True)
    item = models.ForeignKey('Item', on_delete=models.CASCADE, null=True)

以下是我的views.py，特别是引发错误的视图，我已发表评论以进一步帮助确认错误发生的位置

Views.py

# View where the error occurs
def payment_complete(request):
    body = json.loads(request.body)

    order = Order.objects.get(
        user=request.user, ordered=False, ref_code=body['orderid'])
    payment = Payment(
        user=request.user,
        paypal_transaction_id=body['payid'],
        amount=order.get_total()
    )
    payment.save()
    order.ordered = True
    order.payment = payment
    order.received = True
    order.save()
    order_items = order.items.all()
    order_items.update(ordered=True)

    for item in order_items:
        if item.item.is_footwear:\
            # ERROR OCCURS BELOW ---------
            st = StockQuantity.objects.get(
                item=item.item, color=item.color, footwear_size=str(item.footwear_size))
        else:
            # ERROR OCCURS BELOW ---------
            st = StockQuantity.objects.get(
                item=item.item, color=item.color, cloth_size=str(item.cloth_size))
        if st.stock_quantity > 0:
            st.stock_quantity -= item.quantity
            st.save()
            item.save()
            item.item.save()
        else:
            messages.warning("Item out of stock!!")
        print("Quantity " + str(st.stock_quantity))
    # order_item = OrderItem.objects.get(user=request.user, ordered=True)

    messages.success(request, "Order placed successfully!!")
    return redirect("/")

追溯和错误

Django version 3.1.1, using settings 'djecommerce.settings'
Starting development server at http://127.0.0.1:8000/      
Quit the server with CTRL-BREAK.
[25/Nov/2020 11:23:42] "GET /product/dummy-item-1/ HTTP/1.1" 200 15564
[25/Nov/2020 11:23:45] "POST /add-to-cart/dummy-item-1 HTTP/1.1" 302 0
[25/Nov/2020 11:23:45] "GET /order-summary/ HTTP/1.1" 200 9206
[25/Nov/2020 11:23:46] "GET /checkout/ HTTP/1.1" 200 37908
Using the defualt shipping address
Using the defualt billing address
[25/Nov/2020 11:23:51] "POST /checkout/ HTTP/1.1" 302 0
[25/Nov/2020 11:23:51] "GET /payment/paypal/ HTTP/1.1" 200 11866
Internal Server Error: /payment-complete/
Traceback (most recent call last):
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\fields\__init__.py", line 1774, in get_prep_value
    return int(value)
ValueError: invalid literal for int() with base 10: 'S'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\core\handlers\base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\core\views.py", line 446, in payment_complete
    st = StockQuantity.objects.get(
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\query.py", line 418, in get
    clone = self._chain() if self.query.combinator else self.filter(*args, **kwargs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\query.py", line 942, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\query.py", line 962, in _filter_or_exclude
    clone._filter_or_exclude_inplace(negate, *args, **kwargs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\query.py", line 969, in _filter_or_exclude_inplace
    self._query.add_q(Q(*args, **kwargs))
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\sql\query.py", line 1358, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\sql\query.py", line 1377, in _add_q
    child_clause, needed_inner = self.build_filter(
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\sql\query.py", line 1319, in build_filter
    condition = self.build_lookup(lookups, col, value)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\sql\query.py", line 1165, in build_lookup
    lookup = lookup_class(lhs, rhs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\lookups.py", line 24, in __init__
    self.rhs = self.get_prep_lookup()
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\fields\related_lookups.py", line 115, in get_prep_lookup
    self.rhs = target_field.get_prep_value(self.rhs)
  File "C:\Users\halfs\Desktop\DJango\Django-ecommerce\env\lib\site-packages\django\db\models\fields\__init__.py", line 1776, in get_prep_value
    raise e.__class__(
ValueError: Field 'id' expected a number but got 'S'.
[25/Nov/2020 11:24:18] "POST /payment-complete/ HTTP/1.1" 500 129792
[25/Nov/2020 11:24:19] "GET / HTTP/1.1" 200 15371

我知道问题是 Django 通过分配 ID 而不是实际值来保存外键，但如果我不知道对象的 ID，我不知道如何过滤对象。 谢谢，任何帮助表示赞赏！

Answer 1

查询 ForeignKey 字段时，您“通常”传递模型的一个实例。例如：

# Example models
class AnotherModel(models.Model):
    name = models.CharField(...)


class MyModel(models.Model):
    another_model = models.ForeignKey(AnotherModel,...)


# Get the instance
another_model_instance = AnotherModel.objects.get(id=1)
# Use the instance in the query
my_model = MyModel.objects.get(another_model=another_model_instance)

但是，您可以使用 __（双下划线）“跳跃”并查询特定字段。例如：

my_model = MyModel.objects.get(another_model__name='Some name')

在上面的示例中，我们使用AnotherModel 模型上的name 字段进行查询。我们可以使用它来修复您视图中的查询。

# Taken from your payment_complete view
for item in order_items:
    if item.item.is_footwear:
        st = StockQuantity.objects.get(
            item=item.item,
            color__item_color=item.color,
            footwear_size__footwear_size=str(item.footwear_size)
        )
    else:
        st = StockQuantity.objects.get(
            item=item.item,
            color__item_color=item.color,
            cloth_size__cloth_size=str(item.cloth_size)
        )    

延伸阅读：https://docs.djangoproject.com/en/3.1/topics/db/queries/.

Answer 2

对于footwear_size 和cloth_size，您将实际值发送到视图（S、M、L 等），但您的字段是一个外键，它是一个整数。

您需要传递外键值而不是字符串值，或者更改查找以搜索字符串值（类似于footwear_size__name=str(item.footwear_size)）。