Get the latest input from the model

Question

I wanna the last input to bid_price to be received in the Bid_info model and attributed to bid_max, however it gives this error

earliest() and latest() require either fields as positional arguments or 'get_latest_by' in the model's Meta.

views:

@login_required
def page_product(request, productid):
    bid_max = Bid_info.objects.filter(pk=productid).latest()
    context={
        'bid_max' : bid_max      
    }
return render(request, 'auctions/page_product.html', context)

html:

<p> final price = {{bid_max}} </p>

models:

class Bid_info(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    seller = models.ForeignKey(User, on_delete=models.CASCADE, related_name="seller")
    bid_price = models.DecimalField(max_digits=10, decimal_places=2)
    checkclose = models.BooleanField(default=False)
    winner = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, 
                                                                blank=True)

Answer 1

The first problem is what you use to order. You can use the primary key, but that is often a tricky choice: the primary key is not per se assigned in a linear manner.

If you want to get the bid with the largest bid_price, you use:

@login_required
def page_product(request, productid):
    bid_max = Bid_info.objects.filter(product_id=productid).latest('bid_price')
    context = {'bid_max': bid_max}
    return render(request, 'auctions/page_product.html', context)

This will thus return the Bid_info object for the product with the highest bid_price.

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Note: Models in Django are written in PascalCase, not snake_case, so you might want to rename the model from Bid_info to BidInfo.

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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.