I have a question in Django on how you can compare dates to solve some solutions. For example I have a datefield in my models.py Like below.

class Invoice(models.Model):
    payment_date = models.DateTimeField()

What I want to be able to do is ask if the is a way to compare a datetime.now with a DateTimeField. For example, if I had a list of payment dates and I wanted to compare with datetime now. Thhe payment_date's that are late with their payments are shown in owing. Otherwise, it the value is zero.

Here is my views to show whats going on. I have tried so far but I get a 0 value for payment_date's which are later than the payment date.

Edit here is my latest views. Funny thing is that I seem to be getting the owing = invoice_gross for all results - unlike before when I was getting all 0s. So it is still not working properly.

@login_required
def homepage(request):
    invoices_list = Invoice.objects.all()
    invoice_name = invoices_list[0].client_contract_number.client_number.name
    invoice_gross = invoices_list[0].invoice_gross
    payment_date = invoices_list[0].payment_date
    if payment_date <= datetime.now():
        owing = invoice_gross
        if payment_date > datetime.now():
            owing = 0
    return render_to_response(('index.html', locals()), {'invoices_list': invoices_list ,'invoice_name':invoice_name, 'invoice_gross':invoice_gross,'payment_date':payment_date,'owing':owing}, context_instance=RequestContext(request))

Oh and my table is basically doing something like this.

ID  Owing
1   100   (All the same value)
2   100
3   100
.   .
.   .
.   .

I think the problem is in the line

if datetime.now() == payment_date:

That will literally see if the payment_date is right now. I think you want to see if now is greater than or equal to the payment_date, in which case you should use

if datetime.now() >= payment_date:

You can also just filter the invoices when you query the database:

invoices_list = Invoice.objects.filter(payment_date__lte=datetime.now())

Update

Your code is wrong because you have mutually exclusive conditionals. Look:

if payment_date <= datetime.now():
    owing = invoice_gross
    if payment_date > datetime.now():
        owing = 0

That first checks to see if payment_date is before now. Then it sets owing to invoice_gross. Then, in the same conditional, it checks to see if payment_date is after now. But that can't be! You are only in this block of code if payment_date is before now!

I think you have an indentation error, and want this instead:

if payment_date <= datetime.now():
    owing = invoice_gross
if payment_date > datetime.now():
    owing = 0

Which, of course, is the same as:

if payment_date <= datetime.now():
    owing = invoice_gross
else:
    owing = 0

Use datetime.now() (notice the parens). Other than that, remember that the field will always be a datetime object. Also, (I guess that) you should check only the date of the datetime to match the current date (or else it will only match that specific second). For that you have to check if payment_date.date() == date.today() (where date is datetime.date)

This also means that you can filter like this: Invoice.objects.filter(payment_date__lte=datetime.now()).

__lte, __gte, __lt, __gt are used for <=, >=, < and >

来源：https://stackoverflow.com/questions/4606207/using-datetime-to-compare-with-dates-in-django

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