python - 类型错误 : '<=' not supported between instances of 'decimal.Decimal' and 'dict'

Question

我不确定如何解决这个问题。我尝试将 highest_bid 转换为 float :

highest_bid = float(Bid.objects.filter(id=bid_item.id).aggregate(Max('bid_input')))

但这也产生了一个错误，因为字典不能以这种方式转换为 float 。所以我不确定如何解决这个问题。我正在尝试建立一个拍卖网站，如果用户的出价低于上市起拍价且低于所有已出价的最高价，我希望拒绝该出价。

错误

Internal Server Error: /listing/2/bid
Traceback (most recent call last):
  File "C:\Python\Python385\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Python\Python385\lib\site-packages\django\core\handlers\base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\sarah\Desktop\commerce\auctions\views.py", line 157, in placebid
    if bidform.cleaned_data['bid_input'] < listing.start_price and bidform.cleaned_data['bid_input'] <= highest_bid:
TypeError: '<=' not supported between instances of 'decimal.Decimal' and 'dict'
[08/Oct/2020 13:59:48] "POST /listing/2/bid HTTP/1.1" 500 62598

views.py

def placebid(request, id):
    listing_bid = get_object_or_404(Listing, id=id)
    highest_bid = Bid.objects.filter(id=id).aggregate(Max('bid_input'))
    listing = Listing.objects.get(pk=id)
    if request.method == "POST":
        bidform = BidForm(request.POST)
        if bidform.is_valid():
            if bidform.cleaned_data['bid_input'] < listing.start_price and bidform.cleaned_data['bid_input'] <= highest_bid:
                return render(request, "auctions/listingPage.html", {
                    "listing": listing,
                    "error": "Make sure your bid is greater than the start price and current highest bid"
                    })
            else:
                listing_bid.bid_input = bidform.cleaned_data['bid_input']
                listing_bid.bidder = request.user
                listing_bid.bid_item = listing
                listing_bid.time = timezone.now()
                listing_bid.save()
                messages.success(request, 'Bid placed succesfully')
                return HttpResponseRedirect(reverse("listing", args=(id,)))
        else:
            return render(request, "auctions/listingPage.html", {
                "bidform": bidform })
    else:
        bidform = BidForm()
    return render(request, "auctions/listingPage.html", {
        "bidform": bidform })

如果我需要包含更多详细信息，请告诉我。

编辑添加:models.py

class Listing(models.Model):

    class NewManager(models.Manager):
        def get_queryset(self):
            return super().get_queryset().filter(status='active')

    options = (
        ('active', 'Active'),
        ('closed', 'Closed'),
    )

    title = models.CharField(max_length=64)
    description = models.TextField(max_length=64)
    start_price = models.DecimalField(max_digits=9, decimal_places=2, validators=[MinValueValidator(0.99)])
    image = models.URLField(max_length=200, blank=True)
    category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name="listings")
    lister = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, default=None, null=True, blank=True, related_name="lister_user")
    date_added = models.DateTimeField(default=timezone.now)
    status = models.CharField(max_length=10, choices=options, default="active")
    winner = models.ForeignKey('Bid', on_delete=models.CASCADE, null=True, related_name="bid_winner")
    favourites = models.ManyToManyField(User, related_name="favourite", default=None, blank=True)
    objects = models.Manager()
    listingmanager = NewManager()

    def __str__(self): 
        return f"{self.title} ({self.pk}, £{self.start_price}, {self.lister})"


class Bid(models.Model):
    bidder = models.ForeignKey(User, on_delete=models.CASCADE, related_name="bidders")
    bid_item = models.ForeignKey(Listing, on_delete=models.CASCADE, related_name="bid_items", default=None)
    bid_input = models.DecimalField(max_digits=9, decimal_places=2, default=None)
    time = models.DateTimeField(default=timezone.now)

    def __str__(self):
        return f"{self.bidder}, bid amount: {self.bid_input}"

编辑添加:更新 views.py

def placebid(request, id):
    listing_bid = get_object_or_404(Listing, id=id)
    highest_bid = Bid.objects.filter(bid_item_id=id).aggregate(Max('bid_input'))['bid_input__max'] or Decimal('0')
    listing = Listing.objects.get(pk=id)
    if request.method == "POST":
        bidform = BidForm(request.POST)
        if bidform.is_valid():
            if bidform.cleaned_data['bid_input'] < listing.start_price and bidform.cleaned_data['bid_input'] <= highest_bid:
                return render(request, "auctions/listingPage.html", {
                    "listing": listing,
                    "error": "Make sure your bid is greater than the start price and current highest bid"
                })
            else:
                newbid = bidform.save(commit=False)
                newbid.bidder = request.user
                newbid.bid_input = bidform.cleaned_data['bid_input']
                newbid.bid_item = listing_bid
                newbid.time = timezone.now()
                newbid.save()
                messages.success(request, 'Bid placed succesfully')
            return HttpResponseRedirect(reverse("listing", args=(id,)))
        else:
            return render(request, "auctions/listingPage.html", {
                "bidform": bidform })
    else:
        bidform = BidForm()
    return render(request, "auctions/listingPage.html", {
        "bidform": bidform })

Answer 1

highest_bid 是一个将聚合名称映射到值的字典，因此例如 { 'bid_input__max': Decimal('14.25') }，您可以因此通过下标从字典中解包值:

highest_bid = Bid.objects.filter(
    id=id
).aggregate(Max('bid_input'))<b>['bid_input__max']</b>

但这可能不会给您预期的值(value)。您过滤 id=id，这意味着查询集跨越 一个 记录。您可能希望过滤 bid_item_id=id 或类似内容:

highest_bid = Bid.objects.filter(
    <b>bid_item_id=id</b>
).aggregate(Max('bid_input'))['bid_input__max']

根据您的评论，可能还没有出价。在这种情况下，它将返回一个 None。我们可以使用零代替:

highest_bid = Bid.objects.filter(
    bid_item_id=id
).aggregate(Max('bid_input'))['bid_input__max'] <b> or Decimal('0')</b>